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                               DISCOURSES:

                         BIOLOGICAL & GEOLOGICAL

                                 ESSAYS

                                   BY

                            THOMAS H. HUXLEY

                                  1894



PREFACE


The contents of the present volume, with three exceptions, are either
popular lectures, or addresses delivered to scientific bodies with which
I have been officially connected. I am not sure which gave me the more
trouble. For I have not been one of those fortunate persons who are able
to regard a popular lecture as a mere _hors d'oeuvre_, unworthy of being
ranked among the serious efforts of a philosopher; and who keep their
fame as scientific hierophants unsullied by attempts--at least of the
successful sort--to be understanded of the people.

On the contrary, I found that the task of putting the truths learned in
the field, the laboratory and the museum, into language which, without
bating a jot of scientific accuracy shall be generally intelligible,
taxed such scientific and literary faculty as I possessed to the
uttermost; indeed my experience has furnished me with no better
corrective of the tendency to scholastic pedantry which besets all those
who are absorbed in pursuits remote from the common ways of men, and
become habituated to think and speak in the technical dialect of their
own little world, as if there were no other.

If the popular lecture thus, as I believe, finds one moiety of its
justification in the self-discipline of the lecturer, it surely finds the
other half in its effect on the auditory. For though various sadly
comical experiences of the results of my own efforts have led me to
entertain a very moderate estimate of the purely intellectual value of
lectures; though I venture to doubt if more than one in ten of an average
audience carries away an accurate notion of what the speaker has been
driving at; yet is that not equally true of the oratory of the hustings,
of the House of Commons, and even of the pulpit?

Yet the children of this world are wise in their generation; and both the
politician and the priest are justified by results. The living voice has
an influence over human action altogether independent of the intellectual
worth of that which it utters. Many years ago, I was a guest at a great
City dinner. A famous orator, endowed with a voice of rare flexibility
and power; a born actor, ranging with ease through every part, from
refined comedy to tragic unction, was called upon to reply to a toast.
The orator was a very busy man, a charming conversationalist and by no
means despised a good dinner; and, I imagine, rose without having given a
thought to what he was going to say. The rhythmic roll of sound was
admirable, the gestures perfect, the earnestness impressive; nothing was
lacking save sense and, occasionally, grammar. When the speaker sat down
the applause was terrific and one of my neighbours was especially
enthusiastic. So when he had quieted down, I asked him what the orator
had said. And he could not tell me.

That sagacious person John Wesley, is reported to have replied to some
one who questioned the propriety of his adaptation of sacred words to
extremely secular airs, that he did not see why the Devil should be left
in possession of all the best tunes. And I do not see why science should
not turn to account the peculiarities of human nature thus exploited by
other agencies: all the more because science, by the nature of its being,
cannot desire to stir the passions, or profit by the weaknesses, of human
nature. The most zealous of popular lecturers can aim at nothing more
than the awakening of a sympathy for abstract truth, in those who do not
really follow his arguments; and of a desire to know more and better in
the few who do.

At the same time it must be admitted that the popularization of science,
whether by lecture or essay, has its drawbacks. Success in this
department has its perils for those who succeed. The "people who fail"
take their revenge, as we have recently had occasion to observe, by
ignoring all the rest of a man's work and glibly labelling him a more
popularizer. If the falsehood were not too glaring, they would say the
same of Faraday and Helmholtz and Kelvin.

On the other hand, of the affliction caused by persons who think that
what they have picked up from popular exposition qualifies them for
discussing the great problems of science, it may be said, as the Radical
toast said of the power of the Crown in bygone days, that it "has
increased, is increasing, and ought to be diminished." The oddities of
"English as she is spoke" might be abundantly paralleled by those of
"Science as she is misunderstood" in the sermon, the novel, and the
leading article; and a collection of the grotesque travesties of
scientific conceptions, in the shape of essays on such trifles as "the
Nature of Life" and the "Origin of All Things," which reach me, from time
to time, might well be bound up with them.


The tenth essay in this volume unfortunately brought me, I will not say
into collision, but into a position of critical remonstrance with regard
to some charges of physical heterodoxy, brought by my distinguished
friend Lord Kelvin, against British Geology. As President of the
Geological Society of London at that time (1869), I thought I might
venture to plead that we were not such heretics as we seemed to be; and
that, even if we were, recantation would not affect the question of
evolution.

I am glad to see that Lord Kelvin has just reprinted his reply to my
plea,[1] and I refer the reader to it. I shall not presume to question
anything, that on such ripe consideration, Lord Kelvin has to say upon
the physical problems involved. But I may remark that no one can have
asserted more strongly than I have done, the necessity of looking to
physics and mathematics, for help in regard to the earliest history of
the globe. (See pp. 108 and 109 of this volume.)

[Footnote 1: _Popular Lectures and Addresses._ II. Macmillan and Co.
1894.]

And I take the opportunity of repeating the opinion, that, whether what
we call geological time has the lower limit assigned to it by Lord
Kelvin, or the higher assumed by other philosophers; whether the germs of
all living things have originated in the globe itself, or whether they
have been imported on, or in, meteorites from without, the problem of the
origin of those successive Faunae and Florae of the earth, the existence of
which is fully demonstrated by paleontology remains exactly where it was.

For I think it will be admitted, that the germs brought to us by
meteorites, if any, were not ova of elephants, nor of crocodiles; not
cocoa-nuts nor acorns; not even eggs of shell-fish and corals; but only
those of the lowest forms of animal and vegetable life. Therefore, since
it is proved that, from a very remote epoch of geological time, the earth
has been peopled by a continual succession of the higher forms of animals
and plants, these either must have been created, or they have arisen by
evolution. And in respect of certain groups of animals, the well-
established facts of paleontology leave no rational doubt that they arose
by the latter method.

In the second place, there are no data whatever, which justify the
biologist in assigning any, even approximately definite, period of time,
either long or short, to the evolution of one species from another by the
process of variation and selection. In the ninth of the following essays,
I have taken pains to prove that the change of animals has gone on at
very different rates in different groups of living beings; that some
types have persisted with little change from the paleozoic epoch till
now, while others have changed rapidly within the limits of an epoch. In
1862 (see below p. 303, 304) in 1863 (vol. II., p. 461) and again in 1864
(ibid., p. 89-91) I argued, not as a matter of speculation, but, from
paleontological facts, the bearing of which I believe, up to that time,
had not been shown, that any adequate hypothesis of the causes of
evolution must be consistent with progression, stationariness and
retrogression, of the same type at different epochs; of different types
in the same epoch; and that Darwin's hypothesis fulfilled these
conditions.

According to that hypothesis, two factors are at work, variation and
selection. Next to nothing is known of the causes of the former process;
nothing whatever of the time required for the production of a certain
amount of deviation from the existing type. And, as respects selection,
which operates by extinguishing all but a small minority of variations,
we have not the slightest means of estimating the rapidity with which it
does its work. All that we are justified in saying is that the rate at
which it takes place may vary almost indefinitely. If the famous paint-
root of Florida, which kills white pigs but not black ones, were abundant
and certain in its action, black pigs might be substituted for white in
the course of two or three years. If, on the other hand, it was rare and
uncertain in action, the white pigs might linger on for centuries.

T.H. HUXLEY.

HODESLEA, EASTBOURNE,

_April, 1894._



CONTENTS


I

ON A PIECE OF CHALK [1868]
(A Lecture delivered to the working men of Norwich during the meeting of
the British Association.)


II

THE PROBLEMS OF THE DEEP SEA [1878]


III

ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. "CHALLENGER" [1875]


IV

YEAST [1871]


V

ON THE FORMATION OF COAL [1870]
(A Lecture delivered at the Philosophical Institute, Bradford.)


VI

ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS
[1876]
(A Friday evening Lecture delivered at the Royal Institution.)


VII

A LOBSTER; OR, THE STUDY OF ZOOLOGY [1861]
(A Lecture delivered at the South Kensington Museum.)


VIII

BIOGENESIS AND ABIOGENESIS [1870]
(The Presidential Address to the Meeting of the British Association for
the Advancement of Science at Liverpool.)


IX

GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE [1862]
(Address to the Geological Society on behalf of the President by one of
the Secretaries.)


X

GEOLOGICAL REFORM [1869]
(Presidential Address to the Geological Society.)


XI

PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION [1870]
(Presidential Address to the Geological Society.)



I


ON A PIECE OF CHALK

[1868]

If a well were sunk at our feet in the midst of the city of Norwich, the
diggers would very soon find themselves at work in that white substance
almost too soft to be called rock, with which we are all familiar as
"chalk."

Not only here, but over the whole county of Norfolk, the well-sinker
might carry his shaft down many hundred feet without coming to the end of
the chalk; and, on the sea-coast, where the waves have pared away the
face of the land which breasts them, the scarped faces of the high cliffs
are often wholly formed of the same material. Northward, the chalk may be
followed as far as Yorkshire; on the south coast it appears abruptly in
the picturesque western bays of Dorset, and breaks into the Needles of
the Isle of Wight; while on the shores of Kent it supplies that long line
of white cliffs to which England owes her name of Albion.

Were the thin soil which covers it all washed away, a curved band of
white chalk, here broader, and there narrower, might be followed
diagonally across England from Lulworth in Dorset, to Flamborough Head in
Yorkshire--a distance of over 280 miles as the crow flies. From this band
to the North Sea, on the east, and the Channel, on the south, the chalk
is largely hidden by other deposits; but, except in the Weald of Kent and
Sussex, it enters into the very foundation of all the south-eastern
counties.

Attaining, as it does in some places, a thickness of more than a thousand
feet, the English chalk must be admitted to be a mass of considerable
magnitude. Nevertheless, it covers but an insignificant portion of the
whole area occupied by the chalk formation of the globe, much of which
has the same general characters as ours, and is found in detached
patches, some less, and others more extensive, than the English. Chalk
occurs in north-west Ireland; it stretches over a large part of France,--
the chalk which underlies Paris being, in fact, a continuation of that of
the London basin; it runs through Denmark and Central Europe, and extends
southward to North Africa; while eastward, it appears in the Crimea and
in Syria, and may be traced as far as the shores of the Sea of Aral, in
Central Asia. If all the points at which true chalk occurs were
circumscribed, they would lie within an irregular oval about 3,000 miles
in long diameter--the area of which would be as great as that of Europe,
and would many times exceed that of the largest existing inland sea--the
Mediterranean.

Thus the chalk is no unimportant element in the masonry of the earth's
crust, and it impresses a peculiar stamp, varying with the conditions to
which it is exposed, on the scenery of the districts in which it occurs.
The undulating downs and rounded coombs, covered with sweet-grassed turf,
of our inland chalk country, have a peacefully domestic and mutton-
suggesting prettiness, but can hardly be called either grand or
beautiful. But on our southern coasts, the wall-sided cliffs, many
hundred feet high, with vast needles and pinnacles standing out in the
sea, sharp and solitary enough to serve as perches for the wary
cormorant, confer a wonderful beauty and grandeur upon the chalk
headlands. And, in the East, chalk has its share in the formation of some
of the most venerable of mountain ranges, such as the Lebanon.

What is this wide-spread component of the surface of the earth? and
whence did it come?


You may think this no very hopeful inquiry. You may not unnaturally
suppose that the attempt to solve such problems as these can lead to no
result, save that of entangling the inquirer in vague speculations,
incapable of refutation and of verification. If such were really the
case, I should have selected some other subject than a "piece of chalk"
for my discourse. But, in truth, after much deliberation, I have been
unable to think of any topic which would so well enable me to lead you to
see how solid is the foundation upon which some of the most startling
conclusions of physical science rest.

A great chapter of the history of the world is written in the chalk. Few
passages in the history of man can be supported by such an overwhelming
mass of direct and indirect evidence as that which testifies to the truth
of the fragment of the history of the globe, which I hope to enable you
to read, with your own eyes, to-night. Let me add, that few chapters of
human history have a more profound significance for ourselves. I weigh my
words well when I assert, that the man who should know the true history
of the bit of chalk which every carpenter carries about in his breeches-
pocket, though ignorant of all other history, is likely, if he will think
his knowledge out to its ultimate results, to have a truer, and therefore
a better, conception of this wonderful universe, and of man's relation to
it, than the most learned student who is deep-read in the records of
humanity and ignorant of those of Nature.

The language of the chalk is not hard to learn, not nearly so hard as
Latin, if you only want to get at the broad features of the story it has
to tell; and I propose that we now set to work to spell that story out
together.

We all know that if we "burn" chalk the result is quicklime. Chalk, in
fact, is a compound of carbonic acid gas, and lime, and when you make it
very hot the carbonic acid flies away and the lime is left. By this
method of procedure we see the lime, but we do not see the carbonic acid.
If, on the other hand, you were to powder a little chalk and drop it into
a good deal of strong vinegar, there would be a great bubbling and
fizzing, and, finally, a clear liquid, in which no sign of chalk would
appear. Here you see the carbonic acid in the bubbles; the lime,
dissolved in the vinegar, vanishes from sight. There are a great many
other ways of showing that chalk is essentially nothing but carbonic acid
and quicklime. Chemists enunciate the result of all the experiments which
prove this, by stating that chalk is almost wholly composed of "carbonate
of lime."

It is desirable for us to start from the knowledge of this fact, though
it may not seem to help us very far towards what we seek. For carbonate
of lime is a widely-spread substance, and is met with under very various
conditions. All sorts of limestones are composed of more or less pure
carbonate of lime. The crust which is often deposited by waters which
have drained through limestone rocks, in the form of what are called
stalagmites and stalactites, is carbonate of lime. Or, to take a more
familiar example, the fur on the inside of a tea-kettle is carbonate of
lime; and, for anything chemistry tells us to the contrary, the chalk
might be a kind of gigantic fur upon the bottom of the earth-kettle,
which is kept pretty hot below.

Let us try another method of making the chalk tell us its own history. To
the unassisted eye chalk looks simply like a very loose and open kind of
stone. But it is possible to grind a slice of chalk down so thin that you
can see through it--until it is thin enough, in fact, to be examined with
any magnifying power that may be thought desirable. A thin slice of the
fur of a kettle might be made in the same way. If it were examined
microscopically, it would show itself to be a more or less distinctly
laminated mineral substance, and nothing more.

But the slice of chalk presents a totally different appearance when
placed under the microscope. The general mass of it is made up of very
minute granules; but, imbedded in this matrix, are innumerable bodies,
some smaller and some larger, but, on a rough average, not more than a
hundredth of an inch in diameter, having a well-defined shape and
structure. A cubic inch of some specimens of chalk may contain hundreds
of thousands of these bodies, compacted together with incalculable
millions of the granules.

The examination of a transparent slice gives a good notion of the manner
in which the components of the chalk are arranged, and of their relative
proportions. But, by rubbing up some chalk with a brush in water and then
pouring off the milky fluid, so as to obtain sediments of different
degrees of fineness, the granules and the minute rounded bodies may be
pretty well separated from one another, and submitted to microscopic
examination, either as opaque or as transparent objects. By combining the
views obtained in these various methods, each of the rounded bodies may
be proved to be a beautifully-constructed calcareous fabric, made up of a
number of chambers, communicating freely with one another. The chambered
bodies are of various forms. One of the commonest is something like a
badly-grown raspberry, being formed of a number of nearly globular
chambers of different sizes congregated together. It is called
_Globigerina_, and some specimens of chalk consist of little else than
_Globigerinoe_ and granules. Let us fix our attention upon the
_Globigerina_. It is the spoor of the game we are tracking. If we can
learn what it is and what are the conditions of its existence, we shall
see our way to the origin and past history of the chalk.

A suggestion which may naturally enough present itself is, that these
curious bodies are the result of some process of aggregation which has
taken place in the carbonate of lime; that, just as in winter, the rime
on our windows simulates the most delicate and elegantly arborescent
foliage--proving that the mere mineral water may, under certain
conditions, assume the outward form of organic bodies--so this mineral
substance, carbonate of lime, hidden away in the bowels of the earth, has
taken the shape of these chambered bodies. I am not raising a merely
fanciful and unreal objection. Very learned men, in former days, have
even entertained the notion that all the formed things found in rocks are
of this nature; and if no such conception is at present held to be
admissible, it is because long and varied experience has now shown that
mineral matter never does assume the form and structure we find in
fossils. If any one were to try to persuade you that an oyster-shell
(which is also chiefly composed of carbonate of lime) had crystallized
out of sea-water, I suppose you would laugh at the absurdity. Your
laughter would be justified by the fact that all experience tends to show
that oyster-shells are formed by the agency of oysters, and in no other
way. And if there were no better reasons, we should be justified, on like
grounds, in believing that _Globigerina_ is not the product of anything
but vital activity.

Happily, however, better evidence in proof of the organic nature of the
_Globigerinoe_ than that of analogy is forthcoming. It so happens that
calcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk,
are being formed, at the present moment, by minute living creatures,
which flourish in multitudes, literally more numerous than the sands of
the sea-shore, over a large extent of that part of the earth's surface
which is covered by the ocean.

The history of the discovery of these living _Globigerinoe_, and of the
part which they play in rock building, is singular enough. It is a
discovery which, like others of no less scientific importance, has
arisen, incidentally, out of work devoted to very different and
exceedingly practical interests. When men first took to the sea, they
speedily learned to look out for shoals and rocks; and the more the
burthen of their ships increased, the more imperatively necessary it
became for sailors to ascertain with precision the depth of the waters
they traversed. Out of this necessity grew the use of the lead and
sounding line; and, ultimately, marine-surveying, which is the recording
of the form of coasts and of the depth of the sea, as ascertained by the
sounding-lead, upon charts.

At the same time, it became desirable to ascertain and to indicate the
nature of the sea-bottom, since this circumstance greatly affects its
goodness as holding ground for anchors. Some ingenious tar, whose name
deserves a better fate than the oblivion into which it has fallen,
attained this object by "arming" the bottom of the lead with a lump of
grease, to which more or less of the sand or mud, or broken shells, as
the case might be, adhered, and was brought to the surface. But, however
well adapted such an apparatus might be for rough nautical purposes,
scientific accuracy could not be expected from the armed lead, and to
remedy its defects (especially when applied to sounding in great depths)
Lieut. Brooke, of the American Navy, some years ago invented a most
ingenious machine, by which a considerable portion of the superficial
layer of the sea-bottom can be scooped out and brought up from any depth
to which the lead descends. In 1853, Lieut. Brooke obtained mud from the
bottom of the North Atlantic, between Newfoundland and the Azores, at a
depth of more than 10,000 feet, or two miles, by the help of this
sounding apparatus. The specimens were sent for examination to Ehrenberg
of Berlin, and to Bailey of West Point, and those able microscopists
found that this deep-sea mud was almost entirely composed of the
skeletons of living organisms--the greater proportion of these being just
like the _Globigerinoe_ already known to occur in the chalk.

Thus far, the work had been carried on simply in the interests of
science, but Lieut. Brooke's method of sounding acquired a high
commercial value, when the enterprise of laying down the telegraph-cable
between this country and the United States was undertaken. For it became
a matter of immense importance to know, not only the depth of the sea
over the whole line along which the cable was to be laid, but the exact
nature of the bottom, so as to guard against chances of cutting or
fraying the strands of that costly rope. The Admiralty consequently
ordered Captain Dayman, an old friend and shipmate of mine, to ascertain
the depth over the whole line of the cable, and to bring back specimens
of the bottom. In former days, such a command as this might have sounded
very much like one of the impossible things which the young Prince in the
Fairy Tales is ordered to do before he can obtain the hand of the
Princess. However, in the months of June and July, 1857, my friend
performed the task assigned to him with great expedition and precision,
without, so far as I know, having met with any reward of that kind. The
specimens or Atlantic mud which he procured were sent to me to be
examined and reported upon.[1]

[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings in the
North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S.
"Cyclops_." Published by order of the Lords Commissioners of the
Admiralty, 1858. They have since formed the subject of an elaborate
Memoir by Messrs. Parker and Jones, published in the _Philosophical
Transactions_ for 1865.]

The result of all these operations is, that we know the contours and the
nature of the surface-soil covered by the North Atlantic for a distance
of 1,700 miles from east to west, as well as we know that of any part of
the dry land. It is a prodigious plain--one of the widest and most even
plains in the world. If the sea were drained off, you might drive a
waggon all the way from Valentia, on the west coast of Ireland, to
Trinity Bay, in Newfoundland. And, except upon one sharp incline about
200 miles from Valentia, I am not quite sure that it would even be
necessary to put the skid on, so gentle are the ascents and descents upon
that long route. From Valentia the road would lie down-hill for about 200
miles to the point at which the bottom is now covered by 1,700 fathoms of
sea-water. Then would come the central plain, more than a thousand miles
wide, the inequalities of the surface of which would be hardly
perceptible, though the depth of water upon it now varies from 10,000 to
15,000 feet; and there are places in which Mont Blanc might be sunk
without showing its peak above water. Beyond this, the ascent on the
American side commences, and gradually leads, for about 300 miles, to the
Newfoundland shore.

Almost the whole of the bottom of this central plain (which extends for
many hundred miles in a north and south direction) is covered by a fine
mud, which, when brought to the surface, dries into a greyish white
friable substance. You can write with this on a blackboard, if you are so
inclined; and, to the eye, it is quite like very soft, grayish chalk.
Examined chemically, it proves to be composed almost wholly of carbonate
of lime; and if you make a section of it, in the same way as that of the
piece of chalk was made, and view it with the microscope, it presents
innumerable _Globigerinoe_ embedded in a granular matrix. Thus this deep-
sea mud is substantially chalk. I say substantially, because there are a
good many minor differences; but as these have no bearing on the question
immediately before us,--which is the nature of the _Globigerinoe_ of the
chalk,--it is unnecessary to speak of them.

_Globigerinoe_ of every size, from the smallest to the largest, are
associated together in the Atlantic mud, and the chambers of many are
filled by a soft animal matter. This soft substance is, in fact, the
remains of the creature to which the _Globigerinoe_ shell, or rather
skeleton, owes its existence--and which is an animal of the simplest
imaginable description. It is, in fact, a mere particle of living jelly,
without defined parts of any kind--without a mouth, nerves, muscles, or
distinct organs, and only manifesting its vitality to ordinary
observation by thrusting out and retracting from all parts of its
surface, long filamentous processes, which serve for arms and legs. Yet
this amorphous particle, devoid of everything which, in the higher
animals, we call organs, is capable of feeding, growing, and multiplying;
of separating from the ocean the small proportion of carbonate of lime
which is dissolved in sea-water; and of building up that substance into a
skeleton for itself, according to a pattern which can be imitated by no
other known agency.

The notion that animals can live and flourish in the sea, at the vast
depths from which apparently living _Globigerinoe_; have been brought up,
does not agree very well with our usual conceptions respecting the
conditions of animal life; and it is not so absolutely impossible as it
might at first sight appear to be, that the _Globigcrinoe_ of the
Atlantic sea-bottom do not live and die where they are found.

As I have mentioned, the soundings from the great Atlantic plain are
almost entirely made up of _Globigerinoe_, with the granules which have
been mentioned, and some few other calcareous shells; but a small
percentage of the chalky mud--perhaps at most some five per cent. of it--
is of a different nature, and consists of shells and skeletons composed
of silex, or pure flint. These silicious bodies belong partly to the
lowly vegetable organisms which are called _Diatomaceoe_, and partly to
the minute, and extremely simple, animals, termed _Radiolaria_. It is
quite certain that these creatures do not live at the bottom of the
ocean, but at its surface--where they may be obtained in prodigious
numbers by the use of a properly constructed net. Hence it follows that
these silicious organisms, though they are not heavier than the lightest
dust, must have fallen, in some cases, through fifteen thousand feet of
water, before they reached their final resting-place on the ocean floor.
And considering how large a surface these bodies expose in proportion to
their weight, it is probable that they occupy a great length of time in
making their burial journey from the surface of the Atlantic to the
bottom.

But if the _Radiolaria_ and Diatoms are thus rained upon the bottom of
the sea, from the superficial layer of its waters in which they pass
their lives, it is obviously possible that the _Globigerinoe_ may be
similarly derived; and if they were so, it would be much more easy to
understand how they obtain their supply of food than it is at present.
Nevertheless, the positive and negative evidence all points the other
way. The skeletons of the full-grown, deep-sea _Globigerinoe_ are so
remarkably solid and heavy in proportion to their surface as to seem
little fitted for floating; and, as a matter of fact, they are not to be
found along with the Diatoms and _Radiolaria_ in the uppermost stratum of
the open ocean. It has been observed, again, that the abundance of
_Globigerinoe_, in proportion to other organisms, of like kind, increases
with the depth of the sea; and that deep-water _Globigerinoe_ are larger
than those which live in shallower parts of the sea; and such facts
negative the supposition that these organisms have been swept by currents
from the shallows into the deeps of the Atlantic. It therefore seems to
be hardly doubtful that these wonderful creatures live and die at the
depths in which they are found.[2]

[Footnote 2: During the cruise of H.M.S. _Bulldog_, commanded by Sir
Leopold M'Clintock, in 1860, living star-fish were brought up, clinging
to the lowest part of the sounding-line, from a depth of 1,260 fathoms,
midway between Cape Farewell, in Greenland, and the Rockall banks. Dr.
Wallich ascertained that the sea-bottom at this point consisted of the
ordinary _Globigerina_ ooze, and that the stomachs of the star-fishes
were full of _Globigerinoe_. This discovery removes all objections to the
existence of living _Globigerinoe_ at great depths, which are based upon
the supposed difficulty of maintaining animal life under such conditions;
and it throws the burden of proof upon those who object to the
supposition that the _Globigerinoe_ live and die where they are found.]

However, the important points for us are, that the living _Globigerinoe_
are exclusively marine animals, the skeletons of which abound at the
bottom of deep seas; and that there is not a shadow of reason for
believing that the habits of the _Globigerinoe_ of the chalk differed
from those of the existing species. But if this be true, there is no
escaping the conclusion that the chalk itself is the dried mud of an
ancient deep sea.

In working over the soundings collected by Captain Dayman, I was
surprised to find that many of what I have called the "granules" of that
mud were not, as one might have been tempted to think at first, the more
powder and waste of _Globigerinoe_, but that they had a definite form and
size. I termed these bodies "_coccoliths_," and doubted their organic
nature. Dr. Wallich verified my observation, and added the interesting
discovery that, not unfrequently, bodies similar to these "coccoliths"
were aggregated together into spheroids, which lie termed
"_coccospheres_." So far as we knew, these bodies, the nature of which is
extremely puzzling and problematical, were peculiar to the Atlantic
soundings. But, a few years ago, Mr. Sorby, in making a careful
examination of the chalk by means of thin sections and otherwise,
observed, as Ehrenberg had done before him, that much of its granular
basis possesses a definite form. Comparing these formed particles with
those in the Atlantic soundings, he found the two to be identical; and
thus proved that the chalk, like the surroundings, contains these
mysterious coccoliths and coccospheres. Here was a further and most
interesting confirmation, from internal evidence, of the essential
identity of the chalk with modern deep-sea mud. _Globigerinoe_,
coccoliths, and coccospheres are found as the chief constituents of both,
and testify to the general similarity of the conditions under which both
have been formed.[3]

[Footnote 3: I have recently traced out the development of the
"coccoliths" from a diameter of 1/7000th of an inch up to their largest
size (which is about 1/1000th), and no longer doubt that they are
produced by independent organisms, which, like the _Globigerinoe_, live
and die at the bottom of the sea.]

The evidence furnished by the hewing, facing, and superposition of the
stones of the Pyramids, that these structures were built by men, has no
greater weight than the evidence that the chalk was built by
_Globigerinoe_; and the belief that those ancient pyramid-builders were
terrestrial and air-breathing creatures like ourselves, is not better
based than the conviction that the chalk-makers lived in the sea. But as
our belief in the building of the Pyramids by men is not only grounded on
the internal evidence afforded by these structures, but gathers strength
from multitudinous collateral proofs, and is clinched by the total
absence of any reason for a contrary belief; so the evidence drawn from
the _Globigerinoe_ that the chalk is an ancient sea-bottom, is fortified
by innumerable independent lines of evidence; and our belief in the truth
of the conclusion to which all positive testimony tends, receives the
like negative justification from the fact that no other hypothesis has a
shadow of foundation.

It may be worth while briefly to consider a few of these collateral
proofs that the chalk was deposited at the bottom of the sea. The great
mass of the chalk is composed, as we have seen, of the skeletons of
_Globigerinoe_, and other simple organisms, imbedded in granular matter.
Here and there, however, this hardened mud of the ancient sea reveals the
remains of higher animals which have lived and died, and left their hard
parts in the mud, just as the oysters die and leave their shells behind
them, in the mud of the present seas.

There are, at the present day, certain groups of animals which are never
found in fresh waters, being unable to live anywhere but in the sea. Such
are the corals; those corallines which are called _Polyzoa_; those
creatures which fabricate the lamp-shells, and are called _Brachiopoda_;
the pearly _Nautilus_, and all animals allied to it; and all the forms of
sea-urchins and star-fishes. Not only are all these creatures confined to
salt water at the present day; but, so far as our records of the past go,
the conditions of their existence have been the same: hence, their
occurrence in any deposit is as strong evidence as can be obtained, that
that deposit was formed in the sea. Now the remains of animals of all the
kinds which have been enumerated, occur in the chalk, in greater or less
abundance; while not one of those forms of shell-fish which are
characteristic of fresh water has yet been observed in it.

When we consider that the remains of more than three thousand distinct
species of aquatic animals have been discovered among the fossils of the
chalk, that the great majority of them are of such forms as are now met
with only in the sea, and that there is no reason to believe that any one
of them inhabited fresh water--the collateral evidence that the chalk
represents an ancient sea-bottom acquires as great force as the proof
derived from the nature of the chalk itself. I think you will now allow
that I did not overstate my case when I asserted that we have as strong
grounds for believing that all the vast area of dry land, at present
occupied by the chalk, was once at the bottom of the sea, as we have for
any matter of history whatever; while there is no justification for any
other belief.

No less certain it is that the time during which the countries we now
call south-east England, France, Germany, Poland, Russia, Egypt, Arabia,
Syria, were more or less completely covered by a deep sea, was of
considerable duration. We have already seen that the chalk is, in places,
more than a thousand feet thick. I think you will agree with me, that it
must have taken some time for the skeletons of animalcules of a hundredth
of an inch in diameter to heap up such a mass as that. I have said that
throughout the thickness of the chalk the remains of other animals are
scattered. These remains are often in the most exquisite state of
preservation. The valves of the shell-fishes are commonly adherent; the
long spines of some of the sea-urchins, which would be detached by the
smallest jar, often remain in their places. In a word, it is certain that
these animals have lived and died when the place which they now occupy
was the surface of as much of the chalk as had then been deposited; and
that each has been covered up by the layer of _Globigerina_ mud, upon
which the creatures imbedded a little higher up have, in like manner,
lived and died. But some of these remains prove the existence of reptiles
of vast size in the chalk sea. These lived their time, and had their
ancestors and descendants, which assuredly implies time, reptiles being
of slow growth.

There is more curious evidence, again, that the process of covering up,
or, in other words, the deposit of _Globigerina_ skeletons, did not go on
very fast. It is demonstrable that an animal of the cretaceous sea might
die, that its skeleton might lie uncovered upon the sea-bottom long
enough to lose all its outward coverings and appendages by putrefaction;
and that, after this had happened, another animal might attach itself to
the dead and naked skeleton, might grow to maturity, and might itself die
before the calcareous mud had buried the whole.

Cases of this kind are admirably described by Sir Charles Lyell. He
speaks of the frequency with which geologists find in the chalk a
fossilized sea-urchin, to which is attached the lower valve of a
_Crania_. This is a kind of shell-fish, with a shell composed of two
pieces, of which, as in the oyster, one is fixed and the other free.

"The upper valve is almost invariably wanting, though occasionally found
in a perfect state of preservation in the white chalk at some distance.
In this case, we see clearly that the sea-urchin first lived from youth
to age, then died and lost its spines, which were carried away. Then the
young _Crania_ adhered to the bared shell, grew and perished in its turn;
after which, the upper valve was separated from the lower, before the
Echinus became enveloped in chalky mud."[4]

A specimen in the Museum of Practical Geology, in London, still further
prolongs the period which must have elapsed between the death of the sea-
urchin, and its burial by the _Globigerinoe_. For the outward face of the
valve of a _Crania_, which is attached to a sea-urchin, (_Micraster_), is
itself overrun by an incrusting coralline, which spreads thence over more
or less of the surface of the sea-urchin. It follows that, after the
upper valve of the _Crania_ fell off, the surface of the attached valve
must have remained exposed long enough to allow of the growth of the
whole coralline, since corallines do not live embedded in mud.[4]

[Footnote 4: _Elements of Geology_, by Sir Charles Lyell, Bart. F.B.S.,
p. 23.]

The progress of knowledge may, one day, enable us to deduce from such
facts as these the maximum rate at which the chalk can have accumulated,
and thus to arrive at the minimum duration of the chalk period. Suppose
that the valve of the _Cronia_ upon which a coralline has fixed itself in
the way just described, is so attached to the sea-urchin that no part of
it is more than an inch above the face upon which the sea-urchin rests.
Then, as the coralline could not have fixed itself, if the _Crania_ had
been covered up with chalk mud, and could not have lived had itself been
so covered, it follows, that an inch of chalk mud could not have
accumulated within the time between the death and decay of the soft parts
of the sea-urchin and the growth of the coralline to the full size which
it has attained. If the decay of the soft parts of the sea-urchin; the
attachment, growth to maturity, and decay of the _Crania_; and the
subsequent attachment and growth of the coralline, took a year (which is
a low estimate enough), the accumulation of the inch of chalk must have
taken more than a year: and the deposit of a thousand feet of chalk must,
consequently, have taken more than twelve thousand years.

The foundation of all this calculation is, of course, a knowledge of the
length of time the _Crania_ and the coralline needed to attain their full
size; and, on this head, precise knowledge is at present wanting. But
there are circumstances which tend to show, that nothing like an inch of
chalk has accumulated during the life of a _Crania_; and, on any probable
estimate of the length of that life, the chalk period must have had a
much longer duration than that thus roughly assigned to it.

Thus, not only is it certain that the chalk is the mud of an ancient sea-
bottom; but it is no less certain, that the chalk sea existed during an
extremely long period, though we may not be prepared to give a precise
estimate of the length of that period in years. The relative duration is
clear, though the absolute duration may not be definable. The attempt to
affix any precise date to the period at which the chalk sea began, or
ended, its existence, is baffled by difficulties of the same kind. But
the relative age of the cretaceous epoch may be determined with as great
ease and certainty as the long duration of that epoch.

You will have heard of the interesting discoveries recently made, in
various parts of Western Europe, of flint implements, obviously worked
into shape by human hands, under circumstances which show conclusively
that man is a very ancient denizen of these regions. It has been proved
that the whole populations of Europe, whose existence has been revealed
to us in this way, consisted of savages, such as the Esquimaux are now;
that, in the country which is now France, they hunted the reindeer, and
were familiar with the ways of the mammoth and the bison. The physical
geography of France was in those days different from what it is now--the
river Somme, for instance, having cut its bed a hundred feet deeper
between that time and this; and, it is probable, that the climate was
more like that of Canada or Siberia, than that of Western Europe.

The existence of these people is forgotten even in the traditions of the
oldest historical nations. The name and fame of them had utterly vanished
until a few years back; and the amount of physical change which has been
effected since their day renders it more than probable that, venerable as
are some of the historical nations, the workers of the chipped flints of
Hoxne or of Amiens are to them, as they are to us, in point of antiquity.
But, if we assign to these hoar relics of long-vanished generations of
men the greatest age that can possibly be claimed for them, they are not
older than the drift, or boulder clay, which, in comparison with the
chalk, is but a very juvenile deposit. You need go no further than your
own sea-board for evidence of this fact. At one of the most charming
spots on the coast of Norfolk, Cromer, you will see the boulder clay
forming a vast mass, which lies upon the chalk, and must consequently
have come into existence after it. Huge boulders of chalk are, in fact,
included in the clay, and have evidently been brought to the position
they now occupy by the same agency as that which has planted blocks of
syenite from Norway side by side with them.

The chalk, then, is certainly older than the boulder clay. If you ask how
much, I will again take you no further than the same spot upon your own
coasts for evidence. I have spoken of the boulder clay and drift as
resting upon the chalk. That is not strictly true. Interposed between the
chalk and the drift is a comparatively insignificant layer, containing
vegetable matter. But that layer tells a wonderful history. It is full of
stumps of trees standing as they grew. Fir-trees are there with their
cones, and hazel-bushes with their nuts; there stand the stools of oak
and yew trees, beeches and alders. Hence this stratum is appropriately
called the "forest-bed."

It is obvious that the chalk must have been upheaved and converted into
dry land, before the timber trees could grow upon it. As the bolls of
some of these trees are from two to three feet in diameter, it is no less
clear that the dry land thus formed remained in the same condition for
long ages. And not only do the remains of stately oaks and well-grown
firs testify to the duration of this condition of things, but additional
evidence to the same effect is afforded by the abundant remains of
elephants, rhinoceroses, hippopotamuses, and other great wild beasts,
which it has yielded to the zealous search of such men as the Rev. Mr.
Gunn. When you look at such a collection as he has formed, and bethink
you that these elephantine bones did veritably carry their owners about,
and these great grinders crunch, in the dark woods of which the forest-
bed is now the only trace, it is impossible not to feel that they are as
good evidence of the lapse of time as the annual rings of the tree
stumps.

Thus there is a writing upon the wall of cliffs at Cromer, and whoso runs
may read it. It tells us, with an authority which cannot be impeached,
that the ancient sea-bed of the chalk sea was raised up, and remained dry
land, until it was covered with forest, stocked with the great game the
spoils of which have rejoiced your geologists. How long it remained in
that condition cannot be said; but "the whirligig of time brought its
revenges" in those days as in these. That dry land, with the bones and
teeth of generations of long-lived elephants, hidden away among the
gnarled roots and dry leaves of its ancient trees, sank gradually to the
bottom of the icy sea, which covered it with huge masses of drift and
boulder clay. Sea-beasts, such as the walrus, now restricted to the
extreme north, paddled about where birds had twittered among the topmost
twigs of the fir-trees. How long this state of things endured we know
not, but at length it came to an end. The upheaved glacial mud hardened
into the soil of modern Norfolk. Forests grew once more, the wolf and the
beaver replaced the reindeer and the elephant; and at length what we call
the history of England dawned.

Thus you have, within the limits of your own county, proof that the chalk
can justly claim a very much greater antiquity than even the oldest
physical traces of mankind. But we may go further and demonstrate, by
evidence of the same authority as that which testifies to the existence
of the father of men, that the chalk is vastly older than Adam himself.
The Book of Genesis informs us that Adam, immediately upon his creation,
and before the appearance of Eve, was placed in the Garden of Eden. The
problem of the geographical position of Eden has greatly vexed the
spirits of the learned in such matters, but there is one point respecting
which, so far as I know, no commentator has ever raised a doubt. This is,
that of the four rivers which are said to run out of it, Euphrates and
Hiddekel are identical with the rivers now known by the names of
Euphrates and Tigris. But the whole country in which these mighty rivers
take their origin, and through which they run, is composed of rocks which
are either of the same age as the chalk, or of later date. So that the
chalk must not only have been formed, but, after its formation, the time
required for the deposit of these later rocks, and for their upheaval
into dry land, must have elapsed, before the smallest brook which feeds
the swift stream of "the great river, the river of Babylon," began to
flow.


Thus, evidence which cannot be rebutted, and which need not be
strengthened, though if time permitted I might indefinitely increase its
quantity, compels you to believe that the earth, from the time of the
chalk to the present day, has been the theatre of a series of changes as
vast in their amount, as they were slow in their progress. The area on
which we stand has been first sea and then land, for at least four
alternations; and has remained in each of these conditions for a period
of great length.

Nor have these wonderful metamorphoses of sea into land, and of land into
sea, been confined to one corner of England. During the chalk period, or
"cretaceous epoch," not one of the present great physical features of the
globe was in existence. Our great mountain ranges, Pyrenees, Alps,
Himalayas, Andes, have all been upheaved since the chalk was deposited,
and the cretaceous sea flowed over the sites of Sinai and Ararat. All
this is certain, because rocks of cretaceous, or still later, date have
shared in the elevatory movements which gave rise to these mountain
chains; and may be found perched up, in some cases, many thousand feet
high upon their flanks. And evidence of equal cogency demonstrates that,
though, in Norfolk, the forest-bed rests directly upon the chalk, yet it
does so, not because the period at which the forest grew immediately
followed that at which the chalk was formed, but because an immense lapse
of time, represented elsewhere by thousands of feet of rock, is not
indicated at Cromer.

I must ask you to believe that there is no less conclusive proof that a
still more prolonged succession of similar changes occurred, before the
chalk was deposited. Nor have we any reason to think that the first term
in the series of these changes is known. The oldest sea-beds preserved to
us are sands, and mud, and pebbles, the wear and tear of rocks which were
formed in still older oceans.

But, great as is the magnitude of these physical changes of the world,
they have been accompanied by a no less striking series of modifications
in its living inhabitants. All the great classes of animals, beasts of
the field, fowls of the air, creeping things, and things which dwell in
the waters, flourished upon the globe long ages before the chalk was
deposited. Very few, however, if any, of these ancient forms of animal
life were identical with those which now live. Certainly not one of the
higher animals was of the same species as any of those now in existence.
The beasts of the field, in the days before the chalk, were not our
beasts of the field, nor the fowls of the air such as those which the eye
of men has seen flying, unless his antiquity dates infinitely further
back than we at present surmise. If we could be carried back into those
times, we should be as one suddenly set down in Australia before it was
colonized. We should see mammals, birds, reptiles, fishes, insects,
snails, and the like, clearly recognizable as such, and yet not one of
them would be just the same as those with which we are familiar, and many
would be extremely different.

From that time to the present, the population of the world has undergone
slow and gradual, but incessant, changes. There has been no grand
catastrophe--no destroyer has swept away the forms of life of one period,
and replaced them by a totally new creation: but one species has vanished
and another has taken its place; creatures of one type of structure have
diminished, those of another have increased, as time has passed on. And
thus, while the differences between the living creatures of the time
before the chalk and those of the present day appear startling, if placed
side by side, we are led from one to the other by the most gradual
progress, if we follow the course of Nature through the whole series of
those relics of her operations which she has left behind. It is by the
population of the chalk sea that the ancient and the modern inhabitants
of the world are most completely connected. The groups which are dying
out flourish, side by side, with the groups which are now the dominant
forms of life. Thus the chalk contains remains of those strange flying
and swimming reptiles, the pterodactyl, the ichthyosaurus, and the
plesiosaurus, which are found in no later deposits, but abounded in
preceding ages. The chambered shells called ammonites and belemnites,
which are so characteristic of the period preceding the cretaceous, in
like manner die with it.

But, amongst these fading remainders of a previous state of things, are
some very modern forms of life, looking like Yankee pedlars among a tribe
of Red Indians. Crocodiles of modern type appear; bony fishes, many of
them very similar to existing species, almost supplant the forms of fish
which predominate in more ancient seas; and many kinds of living shell-
fish first become known to us in the chalk. The vegetation acquires a
modern aspect. A few living animals are not even distinguishable as
species, from those which existed at that remote epoch. The _Globigerina_
of the present day, for example, is not different specifically from that
of the chalk; and the same maybe said of many other _Foraminifera_. I
think it probable that critical and unprejudiced examination will show
that more than one species of much higher animals have had a similar
longevity; but the only example which I can at present give confidently
is the snake's-head lampshell (_Terebratulina caput serpentis_), which
lives in our English seas and abounded (as _Terebratulina striata_ of
authors) in the chalk.

The longest line of human ancestry must hide its diminished head before
the pedigree of this insignificant shell-fish. We Englishmen are proud to
have an ancestor who was present at the Battle of Hastings. The ancestors
of _Terebratulina caput serpentis_ may have been present at a battle of
_Ichthyosauria_ in that part of the sea which, when the chalk was
forming, flowed over the site of Hastings. While all around has changed,
this _Terebratulina_ has peacefully propagated its species from
generation to generation, and stands to this day, as a living testimony
to the continuity of the present with the past history of the globe.


Up to this moment I have stated, so far as I know, nothing but well-
authenticated facts, and the immediate conclusions which they force upon
the mind. But the mind is so constituted that it does not willingly rest
in facts and immediate causes, but seeks always after a knowledge of the
remoter links in the chain of causation.

Taking the many changes of any given spot of the earth's surface, from
sea to land and from land to sea, as an established fact, we cannot
refrain from asking ourselves how these changes have occurred. And when
we have explained them--as they must be explained--by the alternate slow
movements of elevation and depression which have affected the crust of
the earth, we go still further back, and ask, Why these movements?

I am not certain that any one can give you a satisfactory answer to that
question. Assuredly I cannot. All that can be said, for certain, is, that
such movements are part of the ordinary course of nature, inasmuch as
they are going on at the present time. Direct proof may be given, that
some parts of the land of the northern hemisphere are at this moment
insensibly rising and others insensibly sinking; and there is indirect,
but perfectly satisfactory, proof, that an enormous area now covered by
the Pacific has been deepened thousands of feet, since the present
inhabitants of that sea came into existence. Thus there is not a shadow
of a reason for believing that the physical changes of the globe, in past
times, have been effected by other than natural causes. Is there any more
reason for believing that the concomitant modifications in the forms of
the living inhabitants of the globe have been brought about in other
ways?

Before attempting to answer this question, let us try to form a distinct
mental picture of what has happened in some special case. The crocodiles
are animals which, as a group, have a very vast antiquity. They abounded
ages before the chalk was deposited; they throng the rivers in warm
climates, at the present day. There is a difference in the form of the
joints of the back-bone, and in some minor particulars, between the
crocodiles of the present epoch and those which lived before the chalk;
but, in the cretaceous epoch, as I have already mentioned, the crocodiles
had assumed the modern type of structure. Notwithstanding this, the
crocodiles of the chalk are not identically the same as those which lived
in the times called "older tertiary," which succeeded the cretaceous
epoch; and the crocodiles of the older tertiaries are not identical with
those of the newer tertiaries, nor are these identical with existing
forms. I leave open the question whether particular species may have
lived on from epoch to epoch. But each epoch has had its peculiar
crocodiles; though all, since the chalk, have belonged to the modern
type, and differ simply in their proportions, and in such structural
particulars as are discernible only to trained eyes.

How is the existence of this long succession of different species of
crocodiles to be accounted for? Only two suppositions seem to be open to
us--Either each species of crocodile has been specially created, or it
has arisen out of some pre-existing form by the operation of natural
causes. Choose your hypothesis; I have chosen mine. I can find no
warranty for believing in the distinct creation of a score of successive
species of crocodiles in the course of countless ages of time. Science
gives no countenance to such a wild fancy; nor can even the perverse
ingenuity of a commentator pretend to discover this sense, in the simple
words in which the writer of Genesis records the proceedings of the fifth
and six days of the Creation.

On the other hand, I see no good reason for doubting the necessary
alternative, that all these varied species have been evolved from pre-
existing crocodilian forms, by the operation of causes as completely a
part of the common order of nature as those which have effected the
changes of the inorganic world. Few will venture to affirm that the
reasoning which applies to crocodiles loses its force among other
animals, or among plants. If one series of species has come into
existence by the operation of natural causes, it seems folly to deny that
all may have arisen in the same way.

A small beginning has led us to a great ending. If I were to put the bit
of chalk with which we started into the hot but obscure flame of burning
hydrogen, it would presently shine like the sun. It seems to me that this
physical metamorphosis is no false image of what has been the result of
our subjecting it to a jet of fervent, though nowise brilliant, thought
to-night. It has become luminous, and its clear rays, penetrating the
abyss of the remote past, have brought within our ken some stages of the
evolution of the earth. And in the shifting "without haste, but without
rest" of the land and sea, as in the endless variation of the forms
assumed by living beings, we have observed nothing but the natural
product of the forces originally possessed by the substance of the
universe.



II


THE PROBLEMS OF THE DEEP SEA

[1873]

On the 21st of December, 1872, H.M.S. _Challenger_, an eighteen gun
corvette, of 2,000 tons burden, sailed from Portsmouth harbour for a
three, or perhaps four, years' cruise. No man-of-war ever left that
famous port before with so singular an equipment. Two of the eighteen
sixty-eight pounders of the _Challenger's_ armament remained to enable
her to speak with effect to sea-rovers, haply devoid of any respect for
science, in the remote seas for which she is bound; but the main-deck
was, for the most part, stripped of its war-like gear, and fitted up with
physical, chemical, and biological laboratories; Photography had its dark
cabin; while apparatus for dredging, trawling, and sounding; for
photometers and for thermometers, filled the space formerly occupied by
guns and gun-tackle, pistols and cutlasses.

The crew of the _Challenger_ match her fittings. Captain Nares, his
officers and men, are ready to look after the interests of hydrography,
work the ship, and, if need be, fight her as seamen should; while there
is a staff of scientific civilians, under the general direction of Dr.
Wyville Thomson, F.R.S. (Professor of Natural History in Edinburgh
University by rights, but at present detached for duty _in partibus_),
whose business it is to turn all the wonderfully packed stores of
appliances to account, and to accumulate, before the ship returns to
England, such additions to natural knowledge as shall justify the labour
and cost involved in the fitting out and maintenance of the expedition.

Under the able and zealous superintendence of the Hydrographer, Admiral
Richards, every precaution which experience and forethought could devise
has been taken to provide the expedition with the material conditions of
success; and it would seem as if nothing short of wreck or pestilence,
both most improbable contingencies, could prevent the _Challenger_ from
doing splendid work, and opening up a new era in the history of
scientific voyages.

The dispatch of this expedition is the culmination of a series of such
enterprises, gradually increasing in magnitude and importance, which the
Admiralty, greatly to its credit, has carried out for some years past;
and the history of which is given by Dr. Wyville Thomson in the
beautifully illustrated volume entitled "The Depths of the Sea,"
published since his departure.

"In the spring of the year 1868, my friend Dr. W.B. Carpenter, at that
time one of the Vice-Presidents of the Royal Society, was with me in
Ireland, where we were working out together the structure and development
of the Crinoids. I had long previously had a profound conviction that the
land of promise for the naturalist, the only remaining region where there
were endless novelties of extraordinary interest ready to the hand which
had the means of gathering them, was the bottom of the deep sea. I had
even had a glimpse of some of these treasures, for I had seen, the year
before, with Prof. Sars, the forms which I have already mentioned dredged
by his son at a depth of 300 to 400 fathoms off the Loffoten Islands. I
propounded my views to my fellow-labourer, and we discussed the subject
many times over our microscopes. I strongly urged Dr. Carpenter to use
his influence at head-quarters to induce the Admiralty, probably through
the Council of the Royal Society, to give us the use of a vessel properly
fitted with dredging gear and all necessary scientific apparatus, that
many heavy questions as to the state of things in the depths of the
ocean, which were still in a state of uncertainty, might be definitely
settled. After full consideration, Dr. Carpenter promised his hearty co-
operation, and we agreed that I should write to him on his return to
London, indicating generally the results which I anticipated, and
sketching out what I conceived to be a promising line of inquiry. The
Council of the Royal Society warmly supported the proposal; and I give
here in chronological order the short and eminently satisfactory
correspondence which led to the Admiralty placing at the disposal of Dr.
Carpenter and myself the gunboat _Lightninq_, under the command of Staff-
Commander May, R.N., in the summer of 1868, for a trial cruise to the
North of Scotland, and afterwards to the much wider surveys in H.M.S.
_Porcupine_, Captain Calver, R.N., which were made with the additional
association of Mr. Gwyn Jeffreys, in the summers of the years 1869 and
1870."[1]

[Footnote 1: The Depths of the Sea, pp. 49-50.]

Plain men may be puzzled to understand why Dr. Wyville Thomson, not being
a cynic, should relegate the "Land of Promise" to the bottom of the deep
sea, they may still more wonder what manner of "milk and honey" the
_Challenger_ expects to find; and their perplexity may well rise to its
maximum, when they seek to divine the manner in which that milk and honey
are to be got out of so inaccessible a Canaan. I will, therefore,
endeavour to give some answer to these questions in an order the reverse
of that in which I have stated them.

Apart from hooks, and lines, and ordinary nets, fishermen have, from time
immemorial, made use of two kinds of implements for getting at sea-
creatures which live beyond tide-marks--these are the "dredge" and the
"trawl." The dredge is used by oyster-fishermen. Imagine a large bag, the
mouth of which has the shape of an elongated parallelogram, and is
fastened to an iron frame of the same shape, the two long sides of this
rim being fashioned into scrapers. Chains attach the ends of the frame to
a stout rope, so that when the bag is dragged along by the rope the edge
of one of the scrapers rests on the ground, and scrapes whatever it
touches into the bag. The oyster-dredger takes one of these machines in
his boat, and when he has reached the oyster-bed the dredge is tossed
overboard; as soon as it has sunk to the bottom the rope is paid out
sufficiently to prevent it from pulling the dredge directly upwards, and
is then made fast while the boat goes ahead. The dredge is thus dragged
along and scrapes oysters and other sea-animals and plants, stones, and
mud into the bag. When the dredger judges it to be full he hauls it up,
picks out the oysters, throws the rest overboard, and begins again.

Dredging in shallow water, say ten to twenty fathoms, is an easy
operation enough; but the deeper the dredger goes, the heavier must be
his vessel, and the stouter his tackle, while the operation of hauling up
becomes more and more laborious. Dredging in 150 fathoms is very hard
work, if it has to be carried on by manual labour; but by the use of the
donkey-engine to supply power,[2] and of the contrivances known as
"accumulators," to diminish the risk of snapping the dredge rope by the
rolling and pitching of the vessel, the dredge has been worked deeper and
deeper, until at last, on the 22nd of July, 1869, H.M.S. _Porcupine_
being in the Bay of Biscay, Captain Calver, her commander, performed the
unprecedented feat of dredging in 2,435 fathoms, or 14,610 feet, a depth
nearly equal to the height of Mont Blanc. The dredge "was rapidly hauled
on deck at one o'clock in the morning of the 23rd, after an absence of
7-1/4 hours, and a journey of upwards of eight statute miles," with a
hundred weight and a half of solid contents.

[Footnote 2: The emotional side of the scientific nature has its
singularities. Many persons will call to mind a certain philosopher's
tenderness over his watch--"the little creature"--which was so singularly
lost and found again. But Dr. Wyville Thomson surpasses the owner of the
watch in his loving-kindness towards a donkey-engine. "This little engine
was the comfort of our lives. Once or twice it was overstrained, and then
we pitied the willing little thing, panting like an overtaxed horse."]

The trawl is a sort of net for catching those fish which habitually live
at the bottom of the sea, such as soles, plaice, turbot, and gurnett. The
mouth of the net may be thirty or forty feet wide, and one edge of its
mouth is fastened to a beam of wood of the same length. The two ends of
the beam are supported by curved pieces of iron, which raise the beam and
the edge of the net which is fastened to it, for a short distance, while
the other edge of the mouth of the net trails upon the ground. The closed
end of the net has the form of a great pouch; and, as the beam is dragged
along, the fish, roused from the bottom by the sweeping of the net,
readily pass into its mouth and accumulate in the pouch at its end. After
drifting with the tide for six or seven hours the trawl is hauled up, the
marketable fish are picked out, the others thrown away, and the trawl
sent overboard for another operation.

More than a thousand sail of well-found trawlers are constantly engaged
in sweeping the seas around our coast in this way, and it is to them that
we owe a very large proportion of our supply of fish. The difficulty of
trawling, like that of dredging, rapidly increases with the depth at
which the operation is performed; and, until the other day, it is
probable that trawling at so great a depth as 100 fathoms was something
unheard of. But the first news from the _Challenger_ opens up new
possibilities for the trawl.

Dr. Wyville Thomson writes ("Nature," March 20, 1873):--

"For the first two or three hauls in very deep water off the coast of
Portugal, the dredge came up filled with the usual 'Atlantic ooze,'
tenacious and uniform throughout, and the work of hours, in sifting, gave
the very smallest possible result. We were extremely anxious to get some
idea of the general character of the Fauna, and particularly of the
distribution of the higher groups; and after various suggestions for
modification of the dredge, it was proposed to try the ordinary trawl. We
had a compact trawl, with a 15-feet beam, on board, and we sent it down
off Cape St. Vincent at a depth of 600 fathoms. The experiment looked
hazardous, but, to our great satisfaction, the trawl came up all right
and contained, with many of the larger invertebrate, several fishes....
After the first attempt we tried the trawl several times at depths of
1090, 1525, and, finally, 2125 fathoms, and always with success."

To the coral-fishers of the Mediterranean, who seek the precious red
coral, which grows firmly fixed to rocks at a depth of sixty to eighty
fathoms, both the dredge and the trawl would be useless. They, therefore,
have recourse to a sort of frame, to which are fastened long bundles of
loosely netted hempen cord, and which is lowered by a rope to the depth
at which the hempen cords can sweep over the surface of the rocks and
break off the coral, which is brought up entangled in the cords. A
similar contrivance has arisen out of the necessities of deep-sea
exploration.

In the course of the dredging of the _Porcupine_, it was frequently found
that, while few objects of interest were brought up within the dredge,
many living creatures came up sticking to the outside of the dredge-bag,
and even to the first few fathoms of the dredge-rope. The mouth of the
dredge doubtless rapidly filled with mud, and thus the things it should
have brought up were shut out. To remedy this inconvenience Captain
Calver devised an arrangement not unlike that employed by the coral-
fishers. He fastened half a dozen swabs, such as are used for drying
decks, to the dredge. A swab is something like what a birch-broom would
be if its twigs were made of long, coarse, hempen yarns. These dragged
along after the dredge over the surface of the mud, and entangled the
creatures living there--multitudes of which, twisted up in the strands of
the swabs, were brought to the surface with the dredge. A further
improvement was made by attaching a long iron bar to the bottom of the
dredge bag, and fastening large bunches of teased-out hemp to the end of
this bar. These "tangles" bring up immense quantities of such animals as
have long arms, or spines, or prominences which readily become caught in
the hemp, but they are very destructive to the fragile organisms which
they imprison; and, now that the trawl can be successfully worked at the
greatest depths, it may be expected to supersede them; at least, wherever
the ground is soft enough to permit of trawling.

It is obvious that between the dredge, the trawl, and the tangles, there
is little chance for any organism, except such as are able to burrow
rapidly, to remain safely at the bottom of any part of the sea which the
_Challenger_ undertakes to explore. And, for the first time in the
history of scientific exploration, we have a fair chance of learning what
the population of the depths of the sea is like in the most widely
different parts of the world.

And now arises the next question. The means of exploration being fairly
adequate, what forms of life may be looked for at these vast depths?

The systematic study of the Distribution of living beings is the most
modern branch of Biological Science, and came into existence long after
Morphology and Physiology had attained a considerable development. This
naturally does not imply that, from the time men began to observe natural
phenomena, they were ignorant of the fact that the animals and plants of
one part of the world are different from those in other regions; or that
those of the hills are different from those of the plains in the same
region; or finally that some marine creatures are found only in the
shallows, while others inhabit the deeps. Nevertheless, it was only after
the discovery of America that the attention of naturalists was powerfully
drawn to the wonderful differences between the animal population of the
central and southern parts of the new world and that of those parts of
the old world which lie under the same parallels of latitude. So far back
as 1667 Abraham Mylius, in his treatise "De Animalium origine et
migratione, populorum," argues that, since there are innumerable species
of animals in America which do not exist elsewhere, they must have been
made and placed there by the Deity: Buffon no less forcibly insists upon
the difference between the Faunae of the old and new world. But the first
attempt to gather facts of this order into a whole, and to coordinate
them into a series of generalizations, or laws of Geographical
Distribution, is not a century old, and is contained in the "Specimen
Zoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens,"
published, in 1777, by the learned Brunswick Professor, Eberhard
Zimmermann, who illustrates his work by what he calls a "Tabula
Zoographica," which is the oldest distributional map known to me.

In regard to matters of fact, Zimmermann's chief aim is to show that
among terrestrial mammals, some occur all over the world, while others
are restricted to particular areas of greater or smaller extent; and that
the abundance of species follows temperature, being greatest in warm and
least in cold climates. But marine animals, he thinks, obey no such law.
The Arctic and Atlantic seas, he says, are as full of fishes and other
animals as those of the tropics. It is, therefore, clear that cold does
not affect the dwellers in the sea as it does land animals, and that this
must be the case follows from the fact that sea water, "propter varias
quas continet bituminis spiritusque particulas," freezes with much more
difficulty than fresh water. On the other hand, the heat of the
Equatorial sun penetrates but a short distance below the surface of the
ocean. Moreover, according to Zimmermann, the incessant disturbance of
the mass of the sea by winds and tides, so mixes up the warm and the cold
that life is evenly diffused and abundant throughout the ocean.

In 1810, Risso, in his work on the Ichthyology of Nice, laid the
foundation of what has since been termed "bathymetrical" distribution, or
distribution in depth, by showing that regions of the sea bottom of
different depths could be distinguished by the fishes which inhabit them.
There was the _littoral region_ between tide marks with its sand-eels,
pipe fishes, and blennies: the _seaweed region_, extending from low-
water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish;
and the _deep-sea region_, from 450 feet to 1500 feet or more, with
its file-fish, sharks, gurnards, cod, and sword-fish.

More than twenty years later, M.M. Audouin and Milne Edwards carried out
the principle of distinguishing the Faunae of different zones of depth
much more minutely, in their "Recherches pour servir a l'Histoire
Naturelle du Littoral de la France," published in 1832.

They divide the area included between highwater-mark and lowwater-mark of
spring tides (which is very extensive, on account of the great rise and
fall of the tide on the Normandy coast about St. Malo, where their
observations were made) into four zones, each characterized by its
peculiar invertebrate inhabitants. Beyond the fourth region they
distinguish a fifth, which is never uncovered, and is inhabited by
oysters, scallops, and large starfishes and other animals. Beyond this
they seem to think that animal life is absent.[3]

[Footnote 3: "Enfin plus has encore, c'est-a-dire alors loin des cotes,
le fond des eaux ne parait plus etre habite, du moms dans nos mers, par
aucun de ces animaux" (1. c. tom. i. p. 237). The "ces animaux" leaves
the meaning of the authors doubtful.]

Audouin and Milne Edwards were the first to see the importance of the
bearing of a knowledge of the manner in which marine animals are
distributed in depth, on geology. They suggest that, by this means, it
will be possible to judge whether a fossiliferous stratum was formed upon
the shore of an ancient sea, and even to determine whether it was
deposited in shallower or deeper water on that shore; the association of
shells of animals which live in different zones of depth will prove that
the shells have been transported into the position in which they are
found; while, on the other hand, the absence of shells in a deposit will
not justify the conclusion that the waters in which it was formed were
devoid of animal inhabitants, inasmuch as they might have been only too
deep for habitation.

The new line of investigation thus opened by the French naturalists was
followed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our own
country, in 1840,[4] and by Oersted, in Denmark, a few years later. The
genius of Forbes, combined with his extensive knowledge of botany,
invertebrate zoology, and geology, enabled him to do more than any of his
compeers, in bringing the importance of distribution in depth into
notice; and his researches in the Aegean Sea, and still more his
remarkable paper "On the Geological Relations of the existing Fauna and
Flora of the British Isles," published in 1846, in the first volume of
the "Memoirs of the Geological Survey of Great Britain," attracted
universal attention.

[Footnote 4: In the paper in the _Memoirs of the Survey_ cited further
on, Forbes writes:--

"In an essay 'On the Association of Mollusca on the British Coasts,
considered with reference to Pleistocene Geology,' printed in [the
_Edinburgh Academic Annual_ for] 1840, I described the mollusca, as
distributed on our shores and seas, in four great zones or regions,
usually denominated 'The Littoral zone,' 'The region of Laminariae,' 'The
region of Coral-lines,' and 'The region of Corals.' An extensive series
of researches, chiefly conducted by the members of the committee
appointed by the British Association to investigate the marine geology of
Britain by means of the dredge, have not invalidated this classification,
and the researches of Professor Loven, in the Norwegian and Lapland seas,
have borne out their correctness The first two of the regions above
mentioned had been previously noticed by Lamoureux, in his account of the
distribution (vertically) of sea-weeds, by Audouin and Milne Edwards in
their _Observations on the Natural History of the coast of France_, and
by Sars in the preface to his _Beskrivelser og Jagttayelser_."]

On the coasts of the British Islands, Forbes distinguishes four zones or
regions, the Littoral (between tide marks), the Laminarian (between
lowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), and
the Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms).
But, in the deeper waters of the Aegean Sea, between the shore and a depth
of 300 fathoms, Forbes was able to make out no fewer than eight zones of
life, in the course of which the number and variety of forms gradually
diminished until, beyond 300 fathoms, life disappeared altogether. Hence
it appeared as if descent in the sea had much the same effect on life, as
ascent on land. Recent investigations appear to show that Forbes was
right enough in his classification of the facts of distribution in depth
as they are to be observed in the Aegean; and though, at the time he
wrote, one or two observations were extant which might have warned him
not to generalize too extensively from his Aegean experience, his own
dredging work was so much more extensive and systematic than that of any
other naturalist, that it is not wonderful he should have felt justified
in building upon it. Nevertheless, so far as the limit of the range of
life in depth goes, Forbes' conclusion has been completely negatived, and
the greatest depths yet attained show not even an approach to a "zero of
life":--

"During the several cruises of H.M. ships _Lightning_ and _Porcupine_ in
the years 1868, 1869, and 1870," says Dr. Wyville Thomson, "fifty-seven
hauls of the dredge were taken in the Atlantic at depths beyond 500
fathoms, and sixteen at depths beyond 1,000 fathoms, and, in all cases,
life was abundant. In 1869, we took two casts in depths greater than
2,000 fathoms. In both of these life was abundant; and with the deepest
cast, 2,435 fathoms, off the month of the Bay of Biscay, we took living,
well-marked and characteristic examples of all the five invertebrate sub-
kingdoms. And thus the question of the existence of abundant animal life
at the bottom of the sea has been finally settled and for all depths, for
there is no reason to suppose that the depth anywhere exceeds between
three and four thousand fathoms; and if there be nothing in the
conditions of a depth of 2,500 fathoms to prevent the full development of
a varied Fauna, it is impossible to suppose that even an additional
thousand fathoms would make any great difference."[5]

[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind,
obtained by previous observers, are stated at length in the sixth
chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under
the authority of Professor Peirce, the Superintendent of the United
States Coast Survey, in the years 1867, 1868, and 1869, are particularly
noteworthy, and it is probably not too much to say, in the words of
Professor Agassiz, "that we owe to the coast survey the first broad and
comprehensive basis for an exploration of the sea bottom on a large
scale, opening a new era in zoological and geological research."]

As Dr. Wyville Thomson's recent letter, cited above, shows, the use of
the trawl, at great depths, has brought to light a still greater
diversity of life. Fishes came up from a depth of 600 to more than 1,000
fathoms, all in a peculiar condition from the expansion of the air
contained in their bodies. On their relief from the extreme pressure,
their eyes, especially, had a singular appearance, protruding like great
globes from their heads. Bivalve and univalve mollusca seem to be rare at
the greatest depths; but starfishes, sea urchins and other echinoderms,
zoophytes, sponges, and protozoa abound.

It is obvious that the _Challenger_ has the privilege of opening a new
chapter in the history of the living world. She cannot send down her
dredges and her trawls into these virgin depths of the great ocean
without bringing up a discovery. Even though the thing itself may be
neither "rich nor rare," the fact that it came from that depth, in that
particular latitude and longitude, will be a new fact in distribution,
and, as such, have a certain importance.

But it may be confidently assumed that the things brought up will very
frequently be zoological novelties; or, better still, zoological
antiquities, which, in the tranquil and little-changed depths of the
ocean, have escaped the causes of destruction at work in the shallows,
and represent the predominant population of a past age.

It has been seen that Audouin and Milne Edwards foresaw the general
influence of the study of distribution in depth upon the interpretation
of geological phenomena. Forbes connected the two orders of inquiry still
more closely; and in the thoughtful essay "On the connection between the
distribution of the existing Fauna and Flora of the British Isles, and
the geological changes which have affected their area, especially during
the epoch of the Northern drift," to which reference has already been
made, he put forth a most pregnant suggestion.

In certain parts of the sea bottom in the immediate vicinity of the
British Islands, as in the Clyde district, among the Hebrides, in the
Moray Firth, and in the German Ocean, there are depressed areas, forming a
kind of submarine valleys, the centres of which are from 80 to 100
fathoms, or more, deep. These depressions are inhabited by assemblages of
marine animals, which differ from those found over the adjacent and
shallower region, and resemble those which are met with much farther
north, on the Norwegian coast. Forbes called these Scandinavian
detachments "Northern outliers."

How did these isolated patches of a northern population get into these
deep places? To explain the mystery, Forbes called to mind the fact that,
in the epoch which immediately preceded the present, the climate was much
colder (whence the name of "glacial epoch" applied to it); and that the
shells which are found fossil, or sub-fossil, in deposits of that age are
precisely such as are now to be met with only in the Scandinavian, or
still more Arctic, regions. Undoubtedly, during the glacial epoch, the
general population of our seas had, universally, the northern aspect
which is now presented only by the "northern outliers"; just as the
vegetation of the land, down to the sea-level, had the northern character
which is, at present, exhibited only by the plants which live on the tops
of our mountains. But, as the glacial epoch passed away, and the present
climatal conditions were developed, the northern plants were able to
maintain themselves only on the bleak heights, on which southern forms
could not compete with them. And, in like manner, Forbes suggested that,
after the glacial epoch, the northern animals then inhabiting the sea
became restricted to the deeps in which they could hold their own against
invaders from the south, better fitted than they to flourish in the
warmer waters of the shallows. Thus depth in the sea corresponded in its
effect upon distribution to height on the land.

The same idea is applied to the explanation of a similar anomaly in the
Fauna of the Aegean:--

"In the deepest of the regions of depth of the Aegean, the representation
of a Northern Fauna is maintained, partly by identical and partly by
representative forms.... The presence of the latter is essentially due to
the law (of representation of parallels of latitude by zones of depth),
whilst that of the former species depended on their transmission from
their parent seas during a former epoch, and subsequent isolation. That
epoch was doubtless the newer Pliocene or Glacial Era, when the _Mya
truncata_ and other northern forms now extinct in the Mediterranean, and
found fossil in the Sicilian tertiaries, ranged into that sea. The
changes which there destroyed the _shallow water_ glacial forms, did not
affect those living in the depths, and which still survive."[6]

[Footnote 6: _Memoirs of the Geological Survey of Great Britain_, Vol. i.
p. 390.]

The conception that the inhabitants of local depressions of the sea
bottom might be a remnant of the ancient population of the area, which
had held their own in these deep fastnesses against an invading Fauna, as
Britons and Gaels have held out in Wales and in Scotland against
encroaching Teutons, thus broached by Forbes, received a wider
application than Forbes had dreamed of when the sounding machine first
brought up specimens of the mud of the deep sea. As I have pointed out
elsewhere,[7] it at once became obvious that the calcareous sticky mud of
the Atlantic was made up, in the main, of shells of _Globigerina_ and
other _Foraminifera_, identical with those of which the true chalk is
composed, and the identity extended even to the presence of those
singular bodies, the Coccoliths and Coccospheres, the true nature of
which is not yet made out. Here then were organisms, as old as the
cretaceous epoch, still alive, and doing their work of rock-making at the
bottom of existing seas. What if _Globigerina_ and the Coccoliths should
not be the only survivors of a world passed away, which are hidden
beneath three miles of salt water? The letter which Dr. Wyville Thomson
wrote to Dr. Carpenter in May, 1868, out of which all these expeditions
have grown, shows that this query had become a practical problem in Dr.
Thomson's mind at that time; and the desirableness of solving the problem
is put in the foreground of his reasons for urging the Government to
undertake the work of exploration:--

[Footnote 7: See above, "On a Piece of Chalk," p. 13.]

"Two years ago, M. Sars, Swedish Government Inspector of Fisheries, had
an opportunity, in his official capacity, of dredging off the Loffoten
Islands at a depth of 300 fathoms. I visited Norway shortly after his
return, and had an opportunity of studying with his father, Professor
Sars, some of his results. Animal forms were _abundant_; many of them
were new to science; and among them was one of surpassing interest, the
small crinoid, of which you have a specimen, and which we at once
recognised as a degraded type of the _Apiocrinidoe_, an order hitherto
regarded as extinct, which attained its maximum in the Pear Encrinites of
the Jurassic period, and whose latest representative hitherto known was
the _Bourguettocrinus_ of the chalk. Some years previously, Mr.
Absjornsen, dredging in 200 fathoms in the Hardangerfjord, procured
several examples of a Starfish (_Brisinga_), which seems to find its
nearest ally in the fossil genus _Protaster_. These observations place it
beyond a doubt that animal life is abundant in the ocean at depths
varying from 200 to 300 fathoms, that the forms at these great depths
differ greatly from those met with in ordinary dredgings, and that, at
all events in some cases, these animals are closely allied to, and would
seem to be directly descended from, the Fauna of the early tertiaries.

"I think the latter result might almost have been anticipated; and,
probably, further investigation will largely add to this class of data,
and will give us an opportunity of testing our determinations of the
zoological position of some fossil types by an examination of the soft
parts of their recent representatives. The main cause of the destruction,
the migration, and the extreme modification of animal types, appear to be
change of climate, chiefly depending upon oscillations of the earth's
crust. These oscillations do not appear to have ranged, in the Northern
portion of the Northern Hemisphere, much beyond 1,000 feet since the
commencement of the Tertiary Epoch. The temperature of deep waters seems
to be constant for all latitudes at 39 deg.; so that an immense area of the
North Atlantic must have had its conditions unaffected by tertiary or
post-tertiary oscillations."[8]

[Footnote 8: The Depths of the Sea, pp. 51-52.]

As we shall see, the assumption that the temperature of the deep sea is
everywhere 39 deg. F. (4 deg. Cent.) is an error, which Dr. Wyville Thomson
adopted from eminent physical writers; but the general justice of the
reasoning is not affected by this circumstance, and Dr. Thomson's
expectation has been, to some extent, already verified.

Thus besides _Globigerina_, there are eighteen species of deep-sea
_Foraminifera_ identical with species found in the chalk. Imbedded in the
chalky mud of the deep sea, in many localities, are innumerable cup-
shaped sponges, provided with six-rayed silicious spicula, so disposed
that the wall of the cup is formed of a lacework of flinty thread. Not
less abundant, in some parts of the chalk formation, are the fossils
known as _Ventriculites_, well described by Dr. Thomson as "elegant vases
or cups, with branching root-like bases, or groups of regularly or
irregularly spreading tubes delicately fretted on the surface with an
impressed network like the finest lace"; and he adds, "When we compare
such recent forms as _Aphrocallistes, Iphiteon, Holtenia_, and
_Askonema_, with certain series of the chalk _Ventriculites_, there
cannot be the slightest doubt that they belong to the same family--in
some cases to very nearly allied genera."[9]

[Footnote 9: _The Depths of the Sea_, p. 484.]

Professor Duncan finds "several corals from the coast of Portugal more
nearly allied to chalk forms than to any others."

The Stalked Crinoids or Feather Stars, so abundant in ancient times, are
now exclusively confined to the deep sea, and the late explorations have
yielded forms of old affinity, the existence of which has hitherto been
unsuspected. The general character of the group of star fishes imbedded
in the white chalk is almost the same as in the modern Fauna of the deep
Atlantic. The sea urchins of the deep sea, while none of them are
specifically identical with any chalk form, belong to the same general
groups, and some closely approach extinct cretaceous genera.

Taking these facts in conjunction with the positive evidence of the
existence, during the Cretaceous epoch, of a deep ocean where now lies
the dry land of central and southern Europe, northern Africa, and western
and southern Asia; and of the gradual diminution of this ocean during the
older tertiary epoch, until it is represented at the present day by such
teacupfuls as the Caspian, the Black Sea, and the Mediterranean; the
supposition of Dr. Thomson and Dr. Carpenter that what is now the deep
Atlantic, was the deep Atlantic (though merged in a vast easterly
extension) in the Cretaceous epoch, and that the _Globigerina_ mud has
been accumulating there from that time to this, seems to me to have a
great degree of probability. And I agree with Dr. Wyville Thomson against
Sir Charles Lyell (it takes two of us to have any chance against his
authority) in demurring to the assertion that "to talk of chalk having
been uninterruptedly formed in the Atlantic is as inadmissible in a
geographical as in a geological sense."

If the word "chalk" is to be used as a stratigraphical term and
restricted to _Globigerina_ mud deposited during the Cretaceous epoch, of
course it is improper to call the precisely similar mud of more recent
date, chalk. If, on the other hand, it is to be used as a mineralogical
term, I do not see how the modern and the ancient chalks are to be
separated--and, looking at the matter geographically, I see no reason to
doubt that a boring rod driven from the surface of the mud which forms
the floor of the mid-Atlantic would pass through one continuous mass of
_Globigerina_ mud, first of modern, then of tertiary, and then of
mesozoic date; the "chalks" of different depths and ages being
distinguished merely by the different forms of other organisms associated
with the _Globigerinoe_.

On the other hand, I think it must be admitted that a belief in the
continuity of the modern with the ancient chalk has nothing to do with
the proposition that we can, in any sense whatever, be said to be still
living in the Cretaceous epoch. When the _Challenger's_ trawl brings up
an _Ichthyosaurus_, along with a few living specimens of _Belemnites_ and
_Turrilites_, it may be admitted that she has come upon a cretaceous
"outlier." A geological period is characterized not only by the presence
of those creatures which lived in it, but by the absence of those which
have only come into existence later; and, however large a proportion of
true cretaceous forms may be discovered in the deep sea, the modern types
associated with them must be abolished before the Fauna, as a whole,
could, with any propriety, be termed Cretaceous.


I have now indicated some of the chief lines of Biological inquiry, in
which the _Challenger_ has special opportunities for doing good service,
and in following which she will be carrying out the work already
commenced by the _Lightning_ and _Porcupine_ in their cruises of 1868 and
subsequent years.

But biology, in the long run, rests upon physics, and the first condition
for arriving at a sound theory of distribution in the deep sea, is the
precise ascertainment of the conditions of life; or, in other words, a
full knowledge of all those phenomena which are embraced under the head
of the Physical Geography of the Ocean.

Excellent work has already been done in this direction, chiefly under the
superintendence of Dr. Carpenter, by the _Lightning_ and the
_Porcupine_,[10] and some data of fundamental importance to the physical
geography of the sea have been fixed beyond a doubt.

[Footnote 10: _Proceedings of the Royal Society_, 1870 and 1872]

Thus, though it is true that sea-water steadily contracts as it cools
down to its freezing point, instead of expanding before it reaches its
freezing point as fresh water does, the truth has been steadily ignored
by even the highest authorities in physical geography, and the erroneous
conclusions deduced from their erroneous premises have been widely
accepted as if they were ascertained facts. Of course, if sea-water, like
fresh water, were heaviest at a temperature of 39 deg. F. and got lighter as
it approached 32 deg. F., the water of the bottom of the deep sea could not
be colder than 39 deg.. But one of the first results of the careful
ascertainment of the temperature at different depths, by means of
thermometers specially contrived for the avoidance of the errors produced
by pressure, was the proof that, below 1000 fathoms in the Atlantic, down
to the greatest depths yet sounded, the water has a temperature always
lower than 38 deg. Fahr., whatever be the temperature of the water at the
surface. And that this low temperature of the deepest water is probably
the universal rule for the depths of the open ocean is shown, among
others, by Captain Chimmo's recent observations in the Indian ocean,
between Ceylon and Sumatra, where, the surface water ranging from 85 deg.-81 deg.
Fahr., the temperature at the bottom, at a depth of 2270 to 2656 fathoms,
was only from 34 deg. to 32 deg. Fahr.

As the mean temperature of the superficial layer of the crust of the
earth may be taken at about 50 deg. Fahr., it follows that the bottom layer
of the deep sea in temperate and hot latitudes, is, on the average, much
colder than either of the bodies with which it is in contact; for the
temperature of the earth is constant, while that of the air rarely falls
so low as that of the bottom water in the latitudes in question; and even
when it does, has time to affect only a comparatively thin stratum of the
surface water before the return of warm weather.

How does this apparently anomalous state of things come about? If we
suppose the globe to be covered with a universal ocean, it can hardly be
doubted that the cold of the regions towards the poles must tend to cause
the superficial water of those regions to contract and become
specifically heavier. Under these circumstances, it would have no
alternative but to descend and spread over the sea bottom, while its
place would be taken by warmer water drawn from the adjacent regions.
Thus, deep, cold, polar-equatorial currents, and superficial, warmer,
equatorial-polar currents, would be set up; and as the former would have
a less velocity of rotation from west to east than the regions towards
which they travel, they would not be due southerly or northerly currents,
but south-westerly in the northern hemisphere, and north-westerly in the
southern; while, by a parity of reasoning, the equatorial-polar warm
currents would be north-easterly in the northern hemisphere, and south-
easterly in the southern. Hence, as a north-easterly current has the same
direction as a south-westerly wind, the direction of the northern
equatorial-polar current in the extra-tropical part of its course would
pretty nearly coincide with that of the anti-trade winds. The freezing of
the surface of the polar sea would not interfere with the movement thus
set up. For, however bad a conductor of heat ice may be, the unfrozen
sea-water immediately in contact with the undersurface of the ice must
needs be colder than that further off; and hence will constantly tend to
descend through the subjacent warmer water.

In this way, it would seem inevitable that the surface waters of the
northern and southern frigid zones must, sooner or later, find their way
to the bottom of the rest of the ocean; and there accumulate to a
thickness dependent on the rate at which they absorb heat from the crust
of the earth below, and from the surface water above.

If this hypothesis be correct, it follows that, if any part of the ocean
in warm latitudes is shut off from the influence of the cold polar
underflow, the temperature of its deeps should be less cold than the
temperature of corresponding depths in the open sea. Now, in the
Mediterranean, Nature offers a remarkable experimental proof of just the
kind needed. It is a landlocked sea which runs nearly east and west,
between the twenty-ninth and forty-fifth parallels of north latitude.
Roughly speaking, the average temperature of the air over it is 75 deg. Fahr.
in July and 48 deg. in January.

This great expanse of water is divided by the peninsula of Italy
(including Sicily), continuous with which is a submarine elevation
carrying less than 1,200 feet of water, which extends from Sicily to Cape
Bon in Africa, into two great pools--an eastern and a western. The
eastern pool rapidly deepens to more than 12,000 feet, and sends off to
the north its comparatively shallow branches, the Adriatic and the Aegean
Seas. The western pool is less deep, though it reaches some 10,000 feet.
And, just as the western end of the eastern pool communicates by a
shallow passage, not a sixth of its greatest depth, with the western
pool, so the western pool is separated from the Atlantic by a ridge which
runs between Capes Trafalgar and Spartel, on which there is hardly 1,000
feet of water. All the water of the Mediterranean which lies deeper than
about 150 fathoms, therefore, is shut off from that of the Atlantic, and
there is no communication between the cold layer of the Atlantic (below
1,000 fathoms) and the Mediterranean. Under these circumstances, what is
the temperature of the Mediterranean? Everywhere below 600 feet it is
about 55 deg. Fahr.; and consequently, at its greatest depths, it is some 20 deg.
warmer than the corresponding depths of the Atlantic.

It seems extremely difficult to account for this difference in any other
way, than by adopting the views so strongly and ably advocated by Dr.
Carpenter, that, in the existing distribution of land and water, such a
circulation of the water of the ocean does actually occur, as
theoretically must occur, in the universal ocean, with which we started.

It is quite another question, however, whether this theoretic
circulation, true cause as it may be, is competent to give rise to such
movements of sea-water, in mass, as those currents, which have commonly
been regarded as northern extensions of the Gulf-stream. I shall not
venture to touch upon this complicated problem; but I may take occasion
to remark that the cause of a much simpler phenomenon--the stream of
Atlantic water which sets through the Straits of Gibraltar, eastward, at
the rate of two or three miles an hour or more, does not seem to be so
clearly made out as is desirable.

The facts appear to be that the water of the Mediterranean is very
slightly denser than that of the Atlantic (1.0278 to 1.0265), and that
the deep water of the Mediterranean is slightly denser than that of the
surface; while the deep water of the Atlantic is, if anything, lighter
than that of the surface. Moreover, while a rapid superficial current is
setting in (always, save in exceptionally violent easterly winds) through
the Straits of Gibraltar, from the Atlantic to the Mediterranean, a deep
undercurrent (together with variable side currents) is setting out
through the Straits, from the Mediterranean to the Atlantic.

Dr. Carpenter adopts, without hesitation, the view that the cause of this
indraught of Atlantic water is to be sought in the much more rapid
evaporation which takes place from the surface of the Mediterranean than
from that of the Atlantic; and thus, by lowering the level of the former,
gives rise to an indraught from the latter.

But is there any sound foundation for the three assumptions involved
here? Firstly, that the evaporation from the Mediterranean, as a whole,
is much greater than that from the Atlantic under corresponding
parallels; secondly, that the rainfall over the Mediterranean makes up
for evaporation less than it does over the Atlantic; and thirdly,
supposing these two questions answered affirmatively: Are not these
sources of loss in the Mediterranean fully covered by the prodigious
quantity of fresh water which is poured into it by great rivers and
submarine springs? Consider that the water of the Ebro, the Rhine, the
Po, the Danube, the Don, the Dnieper, and the Nile, all flow directly or
indirectly into the Mediterranean; that the volume of fresh water which
they pour into it is so enormous that fresh water may sometimes be baled
up from the surface of the sea off the Delta of the Nile, while the land
is not yet in sight; that the water of the Black Sea is half fresh, and
that a current of three or four miles an hour constantly streams from it
Mediterraneanwards through the Bosphorus;--consider, in addition, that no
fewer than ten submarine springs of fresh water are known to burst up in
the Mediterranean, some of them so large that Admiral Smyth calls them
"subterranean rivers of amazing volume and force"; and it would seem, on
the face of the matter, that the sun must have enough to do to keep the
level of the Mediterranean down; and that, possibly, we may have to seek
for the cause of the small superiority in saline contents of the
Mediterranean water in some condition other than solar evaporation.

Again, if the Gibraltar indraught is the effect of evaporation, why does
it go on in winter as well as in summer?

All these are questions more easily asked than answered; but they must be
answered before we can accept the Gibraltar stream as an example of a
current produced by indraught with any comfort.

The Mediterranean is not included in the _Challenger's_ route, but she
will visit one of the most promising and little explored of
hydrographical regions--the North Pacific, between Polynesia and the
Asiatic and American shores; and doubtless the store of observations upon
the currents of this region, which she will accumulate, when compared
with what we know of the North Atlantic, will throw a powerful light upon
the present obscurity of the Gulf-stream problem.



III


ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. _CHALLLENGER_

[1875]

In May, 1873, I drew attention[1] to the important problems connected
with the physics and natural history of the sea, to the solution of which
there was every reason to hope the cruise of H.M.S. _Challenger_ would
furnish important contributions. The expectation then expressed has not
been disappointed. Reports to the Admiralty, papers communicated to the
Royal Society, and large collections which have already been sent home,
have shown that the _Challenger's_ staff have made admirable use of their
great opportunities; and that, on the return of the expedition in 1874,
their performance will be fully up to the level of their promise. Indeed,
I am disposed to go so far as to say, that if nothing more came of the
_Challengers_ expedition than has hitherto been yielded by her
exploration of the nature of the sea bottom at great depths, a full
scientific equivalent of the trouble and expense of her equipment would
have been obtained.

[Footnote 1: See the preceding Essay.]

In order to justify this assertion, and yet, at the same time, not to
claim more for Professor Wyville Thomson and his colleagues than is their
due, I must give a brief history of the observations which have preceded
their exploration of this recondite field of research, and endeavour to
make clear what was the state of knowledge in December, 1872, and what
new facts have been added by the scientific staff of the _Challenger_. So
far as I have been able to discover, the first successful attempt to
bring up from great depths more of the sea bottom than would adhere to a
sounding-lead, was made by Sir John Ross, in the voyage to the Arctic
regions which he undertook in 1818. In the Appendix to the narrative of
that voyage, there will be found an account of a very ingenious apparatus
called "clams"--a sort of double scoop--of his own contrivance, which Sir
John Ross had made by the ship's armourer; and by which, being in
Baffin's Bay, in 72 deg. 30' N. and 77 deg. 15' W., he succeeded in bringing up
from 1,050 fathoms (or 6,300 feet), "several pounds" of a "fine green
mud," which formed the bottom of the sea in this region. Captain (now Sir
Edward) Sabine, who accompanied Sir John Ross on this cruise, says of
this mud that it was "soft and greenish, and that the lead sunk several
feet into it." A similar "fine green mud" was found to compose the sea
bottom in Davis Straits by Goodsir in 1845. Nothing is certainly known of
the exact nature of the mud thus obtained, but we shall see that the mud
of the bottom of the Antarctic seas is described in curiously similar
terms by Dr. Hooker, and there is no doubt as to the composition of this
deposit.

In 1850, Captain Penny collected in Assistance Bay, in Kingston Bay, and
in Melville Bay, which lie between 73 deg. 45' and 74 deg. 40' N., specimens of
the residuum left by melted surface ice, and of the sea bottom in these
localities. Dr. Dickie, of Aberdeen, sent these materials to Ehrenberg,
who made out[2] that the residuum of the melted ice consisted for the
most part of the silicious cases of diatomaceous plants, and of the
silicious spicula of sponges; while, mixed with these, were a certain
number of the equally silicious skeletons of those low animal organisms,
which were termed _Polycistineoe_ by Ehrenberg, but are now known as
_Radiolaria_.

[Footnote 2: _Ueber neue Anschauungen des kleinsten noerdlichen
Polarlebens_.--Monatsberichte d. K. Akad. Berlin, 1853.]

In 1856, a very remarkable addition to our knowledge of the nature of the
sea bottom in high northern latitudes was made by Professor Bailey of
West Point. Lieutenant Brooke, of the United States Navy, who was
employed in surveying the Sea of Kamschatka, had succeeded in obtaining
specimens of the sea bottom from greater depths than any hitherto
reached, namely from 2,700 fathoms (16,200 feet) in 56 deg. 46' N., and 168 deg.
18' E.; and from 1,700 fathoms (10,200 feet) in 60 deg. 15' N. and 170 deg. 53'
E. On examining these microscopically, Professor Bailey found, as
Ehrenberg had done in the case of mud obtained on the opposite side of
the Arctic region, that the fine mud was made up of shells of
_Diatomacoe_, of spicula of sponges, and of _Radiolaria_, with a small
admixture of mineral matters, but without a trace of any calcareous
organisms.

Still more complete information has been obtained concerning the nature
of the sea bottom in the cold zone around the south pole. Between the
years 1839 and 1843, Sir James Clark Ross executed his famous Antarctic
expedition, in the course of which he penetrated, at two widely distant
points of the Antarctic zone, into the high latitudes of the shores of
Victoria Land and of Graham's Land, and reached the parallel of 80 deg. S.
Sir James Ross was himself a naturalist of no mean acquirements, and Dr.
Hooker,[3] the present President of the Royal Society, accompanied him as
naturalist to the expedition, so that the observations upon the fauna and
flora of the Antarctic regions made during this cruise were sure to have
a peculiar value and importance, even had not the attention of the
voyagers been particularly directed to the importance of noting the
occurrence of the minutest forms of animal and vegetable life in the
ocean.

[Footnote 3: Now Sir Joseph Hooker. 1894.]

Among the scientific instructions for the voyage drawn up by a committee
of the Royal Society, however, there is a remarkable letter from Von
Humboldt to Lord Minto, then First Lord of the Admiralty, in which, among
other things, he dwells upon the significance of the researches into the
microscopic composition of rocks, and the discovery of the great share
which microscopic organisms take in the formation of the crust of the
earth at the present day, made by Ehrenberg in the years 1836-39.
Ehrenberg, in fact, had shown that the extensive beds of "rotten-stone"
or "Tripoli" which occur in various parts of the world, and notably at
Bilin in Bohemia, consisted of accumulations of the silicious cases and
skeletons of _Diatomaceoe_, sponges, and _Radiolaria_; he had proved that
similar deposits were being formed by _Diatomaceoe_, in the pools of the
Thiergarten in Berlin and elsewhere, and had pointed out that, if it were
commercially worth while, rotten-stone might be manufactured by a process
of diatom-culture. Observations conducted at Cuxhaven in 1839, had
revealed the existence, at the surface of the waters of the Baltic, of
living Diatoms and _Radiolaria_ of the same species as those which, in a
fossil state, constitute extensive rocks of tertiary age at Caltanisetta,
Zante, and Oran, on the shores of the Mediterranean.

Moreover, in the fresh-water rotten-stone beds of Bilin, Ehrenberg had
traced out the metamorphosis, effected apparently by the action of
percolating water, of the primitively loose and friable deposit of
organized particles, in which the silex exists in the hydrated or soluble
condition. The silex, in fact, undergoes solution and slow redeposition,
until, in ultimate result, the excessively fine-grained sand, each
particle of which is a skeleton, becomes converted into a dense opaline
stone, with only here and there an indication of an organism.

From the consideration of these facts, Ehrenberg, as early as the year
1839, had arrived at the conclusion that rocks, altogether similar to
those which constitute a large part of the crust of the earth, must be
forming, at the present day, at the bottom of the sea; and he threw out
the suggestion that even where no trace of organic structure is to be
found in the older rocks, it may have been lost by metamorphosis.[4]

[Footnote 4: _Ueber die noch jetzt zahlreich lebende Thierarten der
Kreidebildung und den Organismus der Polythalamien. Abhandlungen der Koen.
Akad. der Wissenchaften._ 1839. _Berlin_. 1841. I am afraid that this
remarkable paper has been somewhat overlooked in the recent discussions
of the relation of ancient rocks to modern deposits.]

The results of the Antarctic exploration, as stated by Dr. Hooker in the
"Botany of the Antarctic Voyage," and in a paper which he read before
the British Association in 1847, are of the greatest importance in
connection with these views, and they are so clearly stated in the former
work, which is somewhat inaccessible, that I make no apology for quoting
them at length--

"The waters and the ice of the South Polar Ocean were alike found to
abound with microscopic vegetables belonging to the order _Diatomaceoe_.
Though much too small to be discernible by the naked eye, they occurred
in such countless myriads as to stain the berg and the pack ice wherever
they were washed by the swell of the sea; and, when enclosed in the
congealing surface of the water, they imparted to the brash and pancake
ice a pale ochreous colour. In the open ocean, northward of the frozen
zone, this order, though no doubt almost universally present, generally
eludes the search of the naturalist; except when its species are
congregated amongst that mucous scum which is sometimes seen floating on
the waves, and of whose real nature we are ignorant; or when the 
contents of the marine animals who feed on these Algae are examined. To
the south, however, of the belt of ice which encircles the globe, between
the parallels of 50 deg. and 70 deg. S., and in the waters comprised between that
belt and the highest latitude ever attained by man, this vegetation is
very conspicuous, from the contrast between its colour and the white snow
and ice in which it is imbedded. Insomuch, that in the eightieth degree,
all the surface ice carried along by the currents, the sides of every
berg and the base of the great Victoria Barrier itself, within reach of
the swell, were tinged brown, as if the polar waters were charged with
oxide of iron.

"As the majority of these plants consist of very simple vegetable cells,
enclosed in indestructible silex (as other Algae are in carbonate of
lime), it is obvious that the death and decomposition of such multitudes
must form sedimentary deposits, proportionate in their extent to the
length and exposure of the coast against which they are washed, in
thickness to the power of such agents as the winds, currents, and sea,
which sweep them more energetically to certain positions, and in purity,
to the depth of the water and nature of the bottom. Hence we detected
their remains along every icebound shore, in the depths of the adjacent
ocean, between 80 and 400 fathoms. Off Victoria Barrier (a perpendicular
wall of ice between one and two hundred feet above the level of the sea)
the bottom of the ocean was covered with a stratum of pure white or green
mud, composed principally of the silicious shells of the _Diatomaceoe_.
These, on being put into water, rendered it cloudy like milk, and took
many hours to subside. In the very deep water off Victoria and Graham's
Land, this mud was particularly pure and fine; but towards the shallow
shores there existed a greater or less admixture of disintegrated rock
and sand; so that the organic compounds of the bottom frequently bore but
a small proportion to the inorganic." ...

"The universal existence of such an invisible vegetation as that of the
Antarctic Ocean, is a truly wonderful fact, and the more from its not
being accompanied by plants of a high order. During the years we spent
there, I had been accustomed to regard the phenomena of life as differing
totally from what obtains throughout all other latitudes, for everything
living appeared to be of animal origin. The ocean swarmed with
_Mollusca_, and particularly entomostracous _Crustacea_, small whales,
and porpoises; the sea abounded with penguins and seals, and the air with
birds; the animal kingdom was ever present, the larger creatures preying
on the smaller, and these again on smaller still; all seemed carnivorous.
The herbivorous were not recognised, because feeding on a microscopic
herbage, of whose true nature I had formed an erroneous impression. It
is, therefore, with no little satisfaction that I now class the
_Diatomaceoe_ with plants, probably maintaining in the South Polar Ocean
that balance between the vegetable and the animal kingdoms which prevails
over the surface of our globe. Nor is the sustenance and nutrition of the
animal kingdom the only function these minute productions may perform;
they may also be the purifiers of the vitiated atmosphere, and thus
execute in the Antarctic latitudes the office of our trees and grass turf
in the temperate regions, and the broad leaves of the palm, &c., in the
tropics." ...

With respect to the distribution of the _Diatomaceoe_, Dr. Hooker
remarks:--

"There is probably no latitude between that of Spitzbergen and Victoria
Land, where some of the species of either country do not exist: Iceland,
Britain, the Mediterranean Sea, North and South America, and the South
Sea Islands, all possess Antarctic _Diatomaceoe_. The silicious coats of
species only known living in the waters of the South Polar Ocean, have,
during past ages, contributed to the formation of rocks; and thus they
outlive several successive creations of organized beings. The phonolite
stones of the Rhine, and the Tripoli stone, contain species identical
with what are now contributing to form a sedimentary deposit (and
perhaps, at some future period, a bed of rock) extending in one
continuous stratum for 400 measured miles. I allude to the shores of the
Victoria Barrier, along whose coast the soundings examined were
invariably charged with diatomaceous remains, constituting a bank which
stretches 200 miles north from the base of Victoria Barrier, while the
average depth of water above it is 300 fathoms, or 1,800 feet. Again,
some of the Antarctic species have been detected floating in the
atmosphere which overhangs the wide ocean between Africa and America. The
knowledge of this marvellous fact we owe to Mr. Darwin, who, when he was
at sea off the Cape de Verd Islands, collected an impalpable powder which
fell on Captain Fitzroy's ship. He transmitted this dust to Ehrenberg,
who ascertained it to consist of the silicious coats, chiefly of American
_Diatomaceoe_, which were being wafted through the upper region of the
air, when some meteorological phenomena checked them in their course and
deposited them on the ship and surface of the ocean.

"The existence of the remains of many species of this order (and amongst
them some Antarctic ones) in the volcanic ashes, pumice, and scoriae of
active and extinct volcanoes (those of the Mediterranean Sea and
Ascension Island, for instance) is a fact bearing immediately upon the
present subject. Mount Erebus, a volcano 12,400 feet high, of the first
class in dimensions and energetic action, rises at once from the ocean in
the seventy-eighth degree of south latitude, and abreast of the
_Diatomaceoe_ bank, which reposes in part on its base. Hence it may not
appear preposterous to conclude that, as Vesuvius receives the waters of
the Mediterranean, with its fish, to eject them by its crater, so the
subterranean and subaqueous forces which maintain Mount Erebus in
activity may occasionally receive organic matter from the bank, and
disgorge it, together with those volcanic products, ashes and pumice.

"Along the shores of Graham's Land and the South Shetland Islands, we
have a parallel combination of igneous and aqueous action, accompanied
with an equally copious supply of _Diatomaceoe_. In the Gulf of Erebus
and Terror, fifteen degrees north of Victoria Land, and placed on the
opposite side of the globe, the soundings were of a similar nature with
those of the Victoria Land and Barrier, and the sea and ice as full of
_Diatomaceoe_. This was not only proved by the deep sea lead, but by the
examination of bergs which, once stranded, had floated off and become
reversed, exposing an accumulation of white friable mud frozen to their
bases, which abounded with these vegetable remains."

The _Challenger_ has explored the Antarctic seas in a region intermediate
between those examined by Sir James Ross's expedition; and the
observations made by Dr. Wyville Thomson and his colleagues in every
respect confirm those of Dr. Hooker:--

"On the 11th of February, lat. 60 deg. 52' S., long. 80 deg. 20' E., and March 3,
lat. 53 deg. 55' S., long. 108 deg. 35' E., the sounding instrument came up
filled with a very fine cream- paste, which scarcely effervesced
with acid, and dried into a very light, impalpable, white powder. This,
when examined under the microscope, was found to consist almost entirely
of the frustules of Diatoms, some of them wonderfully perfect in all the
details of their ornament, and many of them broken up. The species of
Diatoms entering into this deposit have not yet been worked up, but they
appear to be referable chiefly to the genera _Fragillaria, Coscinodiscus,
Choetoceros, Asteromphalus_, and _Dictyocha_, with fragments of the
separated rods of a singular silicious organism, with which we were
unacquainted, and which made up a large proportion of the finer matter of
this deposit. Mixed with the Diatoms there were a few small
_Globigerinoe_, some of the tests and spicules of Radiolarians, and some
sand particles; but these foreign bodies were in too small proportion to
affect the formation as consisting practically of Diatoms alone. On the
4th of February, in lat. 52 deg., 29' S., long., 71 deg. 36" E., a little to the
north of the Heard Islands, the tow-net, dragging a few fathoms below the
surface, came up nearly filled with a pale yellow gelatinous mass. This
was found to consist entirely of Diatoms of the same species as those
found at the bottom. By far the most abundant was the little bundle of
silicious rods, fastened together loosely at one end, separating from one
another at the other end, and the whole bundle loosely twisted into a
spindle. The rods are hollow, and contain the characteristic endochrome
of the _Diatomaceoe_. Like the _Globigerina_ ooze, then, which it
succeeds to the southward in a band apparently of no great width, the
materials of this silicious deposit are derived entirely from the surface
and intermediate depths. It is somewhat singular that Diatoms did not
appear to be in such large numbers on the surface over the Diatom ooze as
they were a little further north. This may perhaps be accounted for by
our not having struck their belt of depth with the tow-net; or it is
possible that when we found it on the 11th of February the bottom deposit
was really shifted a little to the south by the warm current, the
excessively fine flocculent _debris_ of the Diatoms taking a certain time
to sink. The belt of Diatom ooze is certainly a little further to the
southward in long. 83 deg. E., in the path of the reflux of the Agulhas
current, than in long. 108 deg. E.

"All along the edge of the ice-pack--everywhere, in fact, to the south of
the two stations--on the 11th of February on our southward voyage, and on
the 3rd of March on our return, we brought up fine sand and grayish mud,
with small pebbles of quartz and felspar, and small fragments of mica-
slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, I
have no doubt, was derived from the surface like the others, but in this
case by the melting of icebergs and the precipitation of foreign matter
contained in the ice.

"We never saw any trace of gravel or sand, or any material necessarily
derived from land, on an iceberg. Several showed vertical or irregular
fissures filled with discoloured ice or snow; but, when looked at
closely, the discoloration proved usually to be very slight, and the
effect at a distance was usually due to the foreign material filling the
fissure reflecting light less perfectly than the general surface of the
berg. I conceive that the upper surface of one of these great tabular
southern icebergs, including by far the greater part of its bulk, and
culminating in the portion exposed above the surface of the sea, was
formed by the piling up of successive layers of snow during the period,
amounting perhaps to several centuries, during which the ice-cap was
slowly forcing itself over the low land and out to sea over a long extent
of gentle <DW72>, until it reached a depth considerably above 200 fathoms,
when the lower specific weight of the ice caused an upward strain which
at length overcame the cohesion of the mass, and portions were rent off
and floated away. If this be the true history of the formation of these
icebergs, the absence of all land _debris_ in the portion exposed above
the surface of the sea is readily understood. If any such exist, it must
be confined to the lower part of the berg, to that part which has at one
time or other moved on the floor of the ice-cap.

"The icebergs, when they are first dispersed, float in from 200 to 250
fathoms. When, therefore, they have been drifted to latitudes of 65 deg. or
64 deg. S., the bottom of the berg just reaches the layer at which the
temperature of the water is distinctly rising, and it is rapidly melted,
and the mud and pebbles with which it is more or less charged are
precipitated. That this precipitation takes place all over the area where
the icebergs are breaking up, constantly, and to a considerable extent,
is evident from the fact of the soundings being entirely composed of such
deposits; for the Diatoms, _Globigerinoe_, and radiolarians are present
on the surface in large numbers; and unless the deposit from the ice were
abundant it would soon be covered and masked by a layer of the exuvia of
surface organisms."

The observations which have been detailed leave no doubt that the
Antarctic sea bottom, from a little to the south of the fiftieth
parallel, as far as 80 deg. S., is being covered by a fine deposit of
silicious mud, more or less mixed, in some parts, with the ice-borne
_debris_ of polar lands and with the ejections of volcanoes. The
silicious particles which constitute this mud, are derived, in part, from
the diatomaceous plants and radiolarian animals which throng the surface,
and, in part, from the spicula of sponges which live at the bottom. The
evidence respecting the corresponding Arctic area is less complete, but
it is sufficient to justify the conclusion that an essentially similar
silicious cap is being formed around the northern pole.

There is no doubt that the constituent particles of this mud may
agglomerate into a dense rock, such as that formed at Oran on the shores
of the Mediterranean, which is made up of similar materials. Moreover, in
the case of freshwater deposits of this kind it is certain that the
action of percolating water may convert the originally soft and friable,
fine-grained sandstone into a dense, semi-transparent opaline stone, the
silicious organized skeletons being dissolved, and the silex re-deposited
in an amorphous state. Whether such a metamorphosis as this occurs in
submarine deposits, as well as in those formed in fresh water, does not
appear; but there seems no reason to doubt that it may. And hence it may
not be hazardous to conclude that very ordinary metamorphic agencies may
convert these polar caps into a form of quartzite.

In the great intermediate zone, occupying some 110 deg. of latitude, which
separates the circumpolar Arctic and Antarctic areas of silicious
deposit, the Diatoms and _Radiolaria_ of the surface water and the
sponges of the bottom do not die out, and, so far as some forms are
concerned, do not even appear to diminish in total number; though, on a
rough estimate, it would appear that the proportion of _Radiolaria_ to
Diatoms is much greater than in the colder seas. Nevertheless the
composition of the deep-sea mud of this intermediate zone is entirely
different from that of the circumpolar regions.

The first exact information respecting the nature of this mud at depths
greater than 1,000 fathoms was given by Ehrenberg, in the account which
he published in the "Monatsberichte" of the Berlin Academy for the year
1853, of the soundings obtained by Lieut. Berryman, of the United States
Navy, in the North Atlantic, between Newfoundland and the Azores.

Observations which confirm those of Ehrenberg in all essential respects
have been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter,
and Professor Wyville Thomson, in their earlier cruises; and the
continuation of the _Globigerina_ ooze over the South Pacific has been
proved by the recent work of the _Challenger_, by which it is also shown,
for the first time, that, in passing from the equator to high southern
latitudes, the number and variety of the _Foraminifera_ diminishes, and
even the _Globigerinoe_ become dwarfed. And this result, it will be
observed, is in entire accordance with the fact already mentioned that,
in the sea of Kamschatka, the deep-sea mud was found by Bailey to contain
no calcareous organisms.

Thus, in the whole of the "intermediate zone," the silicious deposit
which is being formed there, as elsewhere, by the accumulation of sponge-
spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by the
immensely greater amount of calcareous sediment, which arises from the
aggregation of the skeletons of dead _Foraminifera_. The similarity of
the deposit, thus composed of a large percentage of carbonate of lime,
and a small percentage of silex, to chalk, regarded merely as a kind of
rock, which was first pointed out by Ehrenberg,[5] is now admitted on all
hands; nor can it be reasonably doubted, that ordinary metamorphic
agencies are competent to convert the "modern chalk" into hard limestone
or even into crystalline marble.

[Footnote 5: The following passages in Ehrenberg's memoir on _The
Organisms in the Chalk which are still living_ (1839), are conclusive:--

"7. The dawning period of the existing living organic creation, if such a
period is distinguishable (which is doubtful), can only be supposed to
have existed on the other side of, and below, the chalk formation; and
thus, either the chalk, with its widespread and thick beds, must enter
into the series of newer formations; or some of the accepted four great
geological periods, the quaternary, tertiary, and secondary formations,
contain organisms which still live. It is more probable, in the
proportion of 3 to 1, that the transition or primary period is not
different, but that it is only more difficult to examine and understand,
by reason of the gradual and prolonged chemical decomposition and
metamorphosis of many of its organic constituents."

"10. By the mass-forming _Infasoria_ and _Polythalamia_, secondary are
not distinguishable from tertiary formations; and, from what has been
said, it is possible that, at this very day, rock masses are forming in
the sea, and being raised by volcanic agencies, the constitution of
which, on the whole, is altogether similar to that of the chalk. The
chalk remains distinguishable by its organic remains as a formation, but
not as a kind of rock."]

Ehrenberg appears to have taken it for granted that the _Globigerinoe_
and other _Foraminifera_ which are found in the deep-sea mud, live at the
great depths in which their remains are found; and he supports this
opinion by producing evidence that the soft parts of these organisms are
preserved, and may be demonstrated by removing the calcareous matter with
dilute acids. In 1857, the evidence for and against this conclusion
appeared to me to be insufficient to warrant a positive conclusion one
way or the other, and I expressed myself in my report to the Admiralty on
Captain Dayman's soundings in the following terms:--

"When we consider the immense area over which this deposit is spread, the
depth at which its formation is going on, and its similarity to chalk,
and still more to such rocks as the marls of Caltanisetta, the question,
whence are all these organisms derived? becomes one of high scientific
interest.

"Three answers have suggested themselves:--

"In accordance with the prevalent view of the limitation of life to
comparatively small depths, it is imagined either: 1, that these
organisms have drifted into their present position from shallower waters;
or 2, that they habitually live at the surface of the ocean, and only
fall down into their present position.

"1. I conceive that the first supposition is negatived by the extremely
marked zoological peculiarity of the deep-sea fauna.

"Had the _Globigerinoe_ been drifted into their present position from
shallow water, we should find a very large proportion of the
characteristic inhabitants of shallow waters mixed with them, and this
would the more certainly be the case, as the large _Globigerinoe_, so
abundant in the deep-sea soundings, are, in proportion to their size,
more solid and massive than almost any other _Foraminifera_. But the fact
is that the proportion of other _Foraminifera_ is exceedingly small, nor
have I found as yet, in the deep-sea deposits, any such matters as
fragments of molluscous shells, of _Echini_, &c., which abound in shallow
waters, and are quite as likely to be drifted as the heavy
_Globigerinoe_. Again, the relative proportions of young and fully formed
_Globigerinoe_ seem inconsistent with the notion that they have travelled
far. And it seems difficult to imagine why, had the deposit been
accumulated in this way, _Coscinodisci_ should so almost entirely
represent the _Diatomaceoe_.

"2. The second hypothesis is far more feasible, and is strongly supported
by the fact that many _Polycistineoe [Radiolaria]_ and _Coscinodisci_ are
well known to live at the surface of the ocean. Mr. Macdonald, Assistant-
Surgeon of H.M.S. _Herald_, now in the South-Western Pacific, has lately
sent home some very valuable observations on living forms of this kind,
met with in the stomachs of oceanic mollusks, and therefore certainly
inhabitants of the superficial layer of the ocean. But it is a singular
circumstance that only one of the forms figured by Mr. Macdonald is at
all like a _Globigerina_, and there are some peculiarities about even
this which make me greatly doubt its affinity with that genus. The form,
indeed, is not unlike that of a _Globigerina_, but it is provided with
long radiating processes, of which I have never seen any trace in
_Globigerina_. Did they exist, they might explain what otherwise is a
great objection to this view, viz., how is it conceivable that the heavy
_Globigerina_ should maintain itself at the surface of the water?

"If the organic bodies in the deep-sea soundings have neither been
drifted, nor have fallen from above, there remains but one alternative--
they must have lived and died where they are.

"Important objections, however, at once suggest themselves to this view.
How can animal life be conceived to exist under such conditions of light,
temperature, pressure, and aeration as must obtain at these vast depths?

"To this one can only reply that we know for a certainty that even very
highly-organized animals do continue to live at a depth of 300 and 400
fathoms, inasmuch as they have been dredged up thence; and that the
difference in the amount of light and heat at 400 and at 2,000 fathoms is
probably, so to speak, very far less than the difference in complexity of
organisation between these animals and the humbler _Protozoa_ and
_Protophyta_ of the deep-sea soundings.

"I confess, though as yet far from regarding it proved that the
_Globigerinoe_ live at these depths, the balance of probabilities seems
to me to incline in that direction. And there is one circumstance which
weighs strongly in my mind. It may be taken as a law that any genus of
animals which is found far back in time is capable of living under a
great variety of circumstances as regards light, temperature, and
pressure. Now, the genus _Globigerina_ is abundantly represented in the
cretaceous epoch, and perhaps earlier.

"I abstain, however, at present from drawing any positive conclusions,
preferring rather to await the result of more extended observations."[6]

[Footnote 6: Appendix to Report on Deep-sea Soundings in the Atlantic
Ocean, by Lieut.-Commander Joseph Dayman. 1857.]

Dr. Wallich, Professor Wyville Thomson, and Dr. Carpenter concluded that
the _Globigerinoe_ live at the bottom. Dr. Wallich writes in 1862--"By
sinking very fine gauze nets to considerable depths, I have repeatedly
satisfied myself that _Globigerina_ does not occur in the superficial
strata of the ocean."[7] Moreover, having obtained certain living star-
fish from a depth of 1,260 fathoms, and found their stomachs full of
"fresh-looking _Globigerinoe_" and their _debris_--he adduces this fact
in support of his belief that the _Globigerinoe_ live at the bottom.

[Footnote 7: The _North Atlantic Sea-bed_, p. 137.]

On the other hand, Mueller, Haeckel, Major Owen, Mr. Gwyn Jeffries, and
other observers, found that _Globigerinoe_, with the allied genera
_Orbulina_ and _Pulvinulina_, sometimes occur abundantly at the surface
of the sea, the shells of these pelagic forms being not unfrequently
provided with the long spines noticed by Macdonald; and in 1865 and 1866,
Major Owen more especially insisted on the importance of this fact. The
recent work of the _Challenger_ fully confirms Major Owen's statement. In
the paper recently published in the proceedings of the Royal Society,[8]
from which a quotation has already been made, Professor Wyville Thomson
says:--

"I had formed and expressed a very strong opinion on the matter. It
seemed to me that the evidence was conclusive that the _Foraminifera_
which formed the _Globigerina_ ooze lived on the bottom, and that the
occurrence of individuals on the surface was accidental and exceptional;
but after going into the thing carefully, and considering the mass of
evidence which has been accumulated by Mr. Murray, I now admit that I was
in error; and I agree with him that it may be taken as proved that all
the materials of such deposits, with the exception, of course, of the
remains of animals which we now know to live at the bottom at all depths,
which occur in the deposit as foreign bodies, are derived from the
surface.

[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procured
by the soundings of H.M.S. _Challenger_ during her cruise in the Southern
Seas, in the early part of the year 1874."--_Proceedings of the Royal
Society_, Nov. 26, 1874.]

"Mr. Murray has combined with a careful examination of the soundings a
constant use of the tow-net, usually at the surface, but also at depths
of from ten to one hundred fathoms; and he finds the closest relation to
exist between the surface fauna of any particular locality and the
deposit which is taking place at the bottom. In all seas, from the
equator to the polar ice, the tow-net contains _Globigerinoe_. They are
more abundant and of a larger size in warmer seas; several varieties,
attaining a large size and presenting marked varietal characters, are
found in the intertropical area of the Atlantic. In the latitude of
Kerguelen they are less numerous and smaller, while further south they
are still more dwarfed, and only one variety, the typical _Globigerina
bulloides_, is represented. The living _Globigerinoe_ from the tow-net
are singularly different in appearance from the dead shells we find at
the bottom. The shell is clear and transparent, and each of the pores
which penetrate it is surrounded by a raised crest, the crest round
adjacent pores coalescing into a roughly hexagonal network, so that the
pores appear to lie at the bottom of a hexagonal pit. At each angle of
this hexagon the crest gives off a delicate flexible calcareous spine,
which is sometimes four or five times the diameter of the shell in
length. The spines radiate symmetrically from the direction of the centre
of each chamber of the shell, and the sheaves of long transparent needles
crossing one another in different directions have a very beautiful
effect. The smaller inner chambers of the shell are entirely filled with
an orange-yellow granular sarcode; and the large terminal chamber usually
contains only a small irregular mass, or two or three small masses run
together, of the same yellow sarcode stuck against one side, the
remainder of the chamber being empty. No definite arrangement and no
approach to structure was observed in the sarcode, and no
differentiation, with the exception of round bright-yellow oil-globules,
very much like those found in some of the radiolarians, which are
scattered, apparently irregularly, in the sarcode. We never have been
able to detect, in any of the large number of _Globigerinoe_ which we
have examined, the least trace of pseudopodia, or any extension, in any
form, of the sarcode beyond the shell.

       *       *       *       *       *

"In specimens taken with the tow-net the spines are very usually absent;
but that is probably on account of their extreme tenuity; they are broken
off by the slightest touch. In fresh examples from the surface, the dots
indicating the origin of the lost spines may almost always be made out
with a high power. There are never spines on the _Globigerinoe_ from the
bottom, even in the shallowest water."


There can now be no doubt, therefore, that _Globigerinoe_ live at the top
of the sea; but the question may still be raised whether they do not also
live at the bottom. In favour of this view, it has been urged that the
shells of the _Globigerinoe_ of the surface never possess such thick
walls as those which are fouled at the bottom, but I confess that I doubt
the accuracy of this statement. Again, the occurrence of minute
_Globigerinoe_ in all stages of development, at the greatest depths, is
brought forward as evidence that they live _in situ_. But considering the
extent to which the surface organisms are devoured, without
discrimination of young and old, by _Salpoe_ and the like, it is not
wonderful that shells of all ages should be among the rejectamenta. Nor
can the presence of the soft parts of the body in the shells which form
the _Globigerina_ ooze, and the fact, if it be one, that animals living
at the bottom use them as food, be considered as conclusive evidence that
the _Globigerinoe_ live at the bottom. Such as die at the surface, and
even many of those which are swallowed by other animals, may retain much
of their protoplasmic matter when they reach the depths at which the
temperature sinks to 34 deg. or 32 deg. Fahrenheit, where decomposition must
become exceedingly slow.

Another consideration appears to me to be in favour of the view that the
_Globigerinoe_ and their allies are essentially surface animals. This is
the fact brought out by the _Challenger's_ work, that they have a
southern limit of distribution, which can hardly depend upon anything but
the temperature of the surface water. And it is to be remarked that this
southern limit occurs at a lower latitude in the Antarctic seas than it
does in the North Atlantic. According to Dr. Wallich ("The North Atlantic
Sea Bed," p. 157) _Globigerina_ is the prevailing form in the deposits
between the Faroe Islands and Iceland, and between Iceland and East
Greenland--or, in other words, in a region of the sea-bottom which lies
altogether north of the parallel of 60 deg. N.; while in the southern seas,
the _Globigerinoe_ become dwarfed and almost disappear between 50 deg. and
55 deg. S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_
have vanished in 56 deg. N., so that the persistence of the _Globigerina_
ooze in high latitudes, in the North Atlantic, would seem to depend on
the northward curve of the isothermals peculiar to this region; and it is
difficult to understand how the formation of _Globigerina_ ooze can be
affected by this climatal peculiarity unless it be effected by surface
animals.

Whatever may be the mode of life of the _Foraminifera_, to which the
calcareous element of the deep-sea "chalk" owes its existence, the fact
that it is the chief and most widely spread material of the sea-bottom in
the intermediate zone, throughout both the Atlantic and Pacific Oceans,
and the Indian Ocean, at depths from a few hundred to over two thousand
fathoms, is established. But it is not the only extensive deposit which
is now taking place. In 1853, Count Pourtales, an officer of the United
States Coast Survey, which has done so much for scientific hydrography,
observed, that the mud forming the sea-bottom at depths of one hundred
and fifty fathoms, in 31 deg. 32' N., 79 deg. 35' W., off the Coast of Florida,
was "a mixture, in about equal proportions, of _Globigerinoe_ and black
sand, probably greensand, as it makes a green mark when crushed on
paper." Professor Bailey, examining these grains microscopically, found
that they were casts of the interior cavities of _Foraminifera_,
consisting of a mineral known as _Glauconite_, which is a silicate of
iron and alumina. In these casts the minutest cavities and finest tubes
in the Foraminifer were sornetilnes reproduced in solid counterparts of
the glassy mineral, while the calcareous original had been entirely
dissolved away.

Contemporaneously with these observations, the indefatigable Ehrenberg
had discovered that the "greensands" of the geologist were largely made
up of casts of a similar character, and proved the existence of
_Foraminifera_ at a very ancient geological epoch, by discovering such
casts in a greensand of Lower Silurian age, which occurs near St.
Petersburg.

Subsequently, Messrs. Parker and Jones discovered similar casts in
process of formation, the original shell not having disappeared, in
specimens of the sea-bottom of the Australian seas, brought home by the
late Professor Jukes. And the _Challenger_ has observed a deposit of a
similar character in the course of the Agulhas current, near the Cape of
Good Hope, and in some other localities not yet defined.

It would appear that this infiltration of _Foraminifera_ shells with
_Glauconite_ does not take place at great depths, but rather in what may
be termed a sublittoral region, ranging from a hundred to three hundred
fathoms. It cannot be ascribed to any local cause, for it takes place,
not only over large areas in the Gulf of Mexico and the Coast of Florida,
but in the South Atlantic and in the Pacific. But what are the conditions
which determine its occurrence, and whence the silex, the iron, and the
alumina (with perhaps potash and some other ingredients in small
quantity) of which the _Glauconite_ is composed, proceed, is a point on
which no light has yet been thrown. For the present we must be content
with the fact that, in certain areas of the "intermediate zone,"
greensand is replacing and representing the primitively calcareo-
silicious ooze.

The investigation of the deposits which are now being formed in the basin
of the Mediterranean, by the late Professor Edward Forbes, by Professor
Williamson and more recently by Dr. Carpenter, and a comparison of the
results thus obtained with what is known of the surface fauna, have
brought to light the remarkable fact, that while the surface and the
shallows abound with _Foraminifera_ and other calcareous shelled
organisms, the indications of life become scanty at depths beyond 500 or
600 fathoms, while almost all traces of it disappear at greater depths,
and at 1,000 to 2,000 fathoms the bottom is covered with a fine clay.

Dr. Carpenter has discussed the significance of this remarkable fact, and
he is disposed to attribute the absence of life at great depths, partly
to the absence of any circulation of the water of the Mediterranean at
such depths, and partly to the exhaustion of the oxygen of the water by
the organic matter contained in the fine clay, which he conceives to be
formed by the finest particles of the mud brought down by the rivers
which flow into the Mediterranean.

However this may be, the explanation thus offered of the presence of the
fine mud, and of the absence of organisms which ordinarily live at the
bottom, does not account for the absence of the skeletons of the
organisms which undoubtedly abound at the surface of the Mediterranean;
and it would seem to have no application to the remarkable fact
discovered by the _Challenger_, that in the open Atlantic and Pacific
Oceans, in the midst of the great intermediate zone, and thousands of
miles away from the embouchure of any river, the sea-bottom, at depths
approaching to and beyond 3,000 fathoms, no longer consists of
_Globigerina_ ooze, but of an excessively fine red clay.

Professor Thomson gives the following account of this capital
discovery:--

"According to our present experience, the deposit of _Globigerina_ ooze
is limited to water of a certain depth, the extreme limit of the pure
characteristic formation being placed at a depth of somewhere about 2,250
fathoms. Crossing from these shallower regions occupied by the ooze into
deeper soundings, we find, universally, that the calcareous formation
gradually passes into, and is finally replaced by, an extremely fine pure
clay, which occupies, speaking generally, all depths below 2,500 fathoms,
and consists almost entirely of a silicate of the red oxide of iron and
alumina. The transition is very slow, and extends over several hundred
fathoms of increasing depth; the shells gradually lose their sharpness of
outline, and assume a kind of 'rotten' look and a brownish colour, and
become more and more mixed with a fine amorphous red-brown powder, which
increases steadily in proportion until the lime has almost entirely
disappeared. This brown matter is in the finest possible state of
subdivision, so fine that when, after sifting it to separate any
organisms it might contain, we put it into jars to settle, it remained
for days in suspension, giving the water very much the appearance and
colour of chocolate.

"In indicating the nature of the bottom on the charts, we came, from
experience and without any theoretical considerations, to use three terms
for soundings in deep water. Two of these, Gl. oz. and r. cl., were very
definite, and indicated strongly-marked formations, with apparently but
few characters in common; but we frequently got soundings which we could
not exactly call '_Globigerina_ ooze' or 'red clay,' and before we were
fully aware of the nature of these, we were in the habit of indicating
them as 'grey ooze' (gr. oz.) We now recognise the 'grey ooze' as an
intermediate stage between the _Globigerina_ ooze and the red clay; we
find that on one side, as it were, of an ideal line, the red clay
contains more and more of the material of the calcareous ooze, while on
the other, the ooze is mixed with an increasing proportion of 'red clay.'

"Although we have met with the same phenomenon so frequently, that we
were at length able to predict the nature of the bottom from the depth of
the soundings with absolute certainty for the Atlantic and the Southern
Sea, we had, perhaps, the best opportunity of observing it in our first
section across the Atlantic, between Teneriffe and St. Thomas. The first
four stations on this section, at depths from 1,525 to 2,220 fathoms,
show _Globigerina_ ooze. From the last of these, which is about 300 miles
from Teneriffe, the depth gradually increases to 2,740 fathoms at 500,
and 2,950 fathoms at 750 miles from Teneriffe. The bottom in these two
soundings might have been called 'grey ooze,' for although its nature has
altered entirely from the _Globigerina_ ooze, the red clay into which it
is rapidly passing still contains a considerable admixture of carbonate
of lime.

"The depth goes on increasing to a distance of 1,150 miles from
Teneriffe, when it reaches 3,150 fathoms; there the clay is pure and
smooth, and contains scarcely a trace of lime. From this great depth the
bottom gradually rises, and, with decreasing depth, the grey colour and
the calcareous composition of the ooze return. Three soundings in 2,050,
1,900, and 1,950 fathoms on the 'Dolphin Rise' gave highly characteristic
examples of the _Globigerina_ formation. Passing from the middle plateau
of the Atlantic into the western trough, with depths a little over 3,000
fathoms, the red clay returned in all its purity; and our last sounding,
in 1,420 fathoms, before reaching Sombrero, restored the _Globigerina_
ooze with its peculiar associated fauna.

"This section shows also the wide extension and the vast geological
importance of the red clay formation. The total distance from Teneriffe
to Sombrero is about 2,700 miles. Proceeding from east to west, we have--

About     80 miles of volcanic mud and sand,
  "      350     "    _Globigerina_ ooze,
  "    1,050     "    red clay,
  "      330     "    _Globigerina_ ooze,
  "      850     "    red clay,
  "       40     "    _Globigerina_ ooze;

giving a total of 1,900 miles of red clay to 720 miles of _Globigerina_
ooze.

"The nature and origin of this vast deposit of clay is a question of the
very greatest interest; and although I think there can be no doubt that
it is in the main solved, yet some matters of detail are still involved
in difficulty. My first impression was that it might be the most minutely
divided material, the ultimate sediment produced by the disintegration of
the land, by rivers and by the action of the sea on exposed coasts, and
held in suspension and distributed by ocean currents, and only making
itself manifest in places unoccupied by the _Globigerina_ ooze. Several
circumstances seemed, however, to negative this mode of origin. The
formation seemed too uniform: wherever we met with it, it had the same
character, and it only varied in composition in containing less or more
carbonate of lime.

"Again, the were gradually becoming more and more convinced that all the
important elements of the _Globigerina_ ooze lived on the surface, and it
seemed evident that, so long as the condition on the surface remained the
same, no alteration of contour at the bottom could possibly prevent its
accumulation; and the surface conditions in the Mid-Atlantic were very
uniform, a moderate current of a very equal temperature passing
continuously over elevations and depressions, and everywhere yielding to
the tow-net the ooze-forming _Foraminifera_ in the same proportion. The
Mid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, the
shells of these are constantly mixed with the _Globigerina_ ooze,
sometimes in number sufficient to make up a considerable portion of its
bulk. It is clear that these shells must fall in equal numbers upon the
red clay, but scarcely a trace of one of them is ever brought up by the
dredge on the red clay area. It might be possible to explain the absence
of shell-secreting animals living on the bottom, on the supposition that
the nature of the deposit was injurious to them; but then the idea of a
current sufficiently strong to sweep them away is negatived by the
extreme fineness of the sediment which is being laid down; the absence of
surface shells appears to be intelligible only on the supposition that
they are in some way removed.

"We conclude, therefore, that the 'red clay' is not an additional
substance introduced from without, and occupying certain depressed
regions on account of some law regulating its deposition, but that it is
produced by the removal, by some means or other, over these areas, of the
carbonate of lime, which forms probably about 98 per cent. of the
material of the _Globigerina_ ooze. We can trace, indeed, every
successive stage in the removal of the carbonate of lime in descending
the <DW72> of the ridge or plateau where the _Globigerina_ ooze is
forming, to the region of the clay. We find, first, that the shells of
pteropods and other surface _Mollusca_ which are constantly falling on
the bottom, are absent, or, if a few remain, they are brittle and yellow,
and evidently decaying rapidly. These shells of _Mollusca_ decompose more
easily and disappear sooner than the smaller, and apparently more
delicate, shells of rhizopods. The smaller _Foraminifera_ now give way,
and are found in lessening proportion to the larger; the coccoliths first
lose their thin outer border and then disappear; and the clubs of the
rhabdoliths get worn out of shape, and are last seen, under a high power,
as infinitely minute cylinders scattered over the field. The larger
_Foraminifera_ are attacked, and instead of being vividly white and
delicately sculptured, they become brown and worn, and finally they break
up, each according to its fashion; the chamber-walls of _Globigerina_
fall into wedge-shaped pieces, which quickly disappear, and a thick rough
crust breaks away from the surface of _Orbulina_, leaving a thin inner
sphere, at first beautifully transparent, but soon becoming opaque and
crumbling away.

"In the meantime the proportion of the amorphous 'red clay' to the
calcareous elements of all kinds increases, until the latter disappear,
with the exception of a few scattered shells of the larger
_Foraminifera_, which are still found even in the most characteristic
samples of the 'red clay.'

"There seems to be no room left for doubt that the red clay is
essentially the insoluble residue, the _ash_, as it were, of the
calcareous organisms which form the _Globigerina_ ooze, after the
calcareous matter has been by some means removed. An ordinary mixture of
calcareous _Foraminifera_ with the shells of pteropods, forming a fair
sample of _Globigerina_ ooze from near St. Thomas, was carefully washed,
and subjected by Mr. Buchanan to the action of weak acid; and he found
that there remained after the carbonate of lime had been removed, about 1
per cent. of a reddish mud, consisting of silica, alumina, and the red
oxide of iron. This experiment has been frequently repeated with
different samples of _Globigerina_ ooze, and always with the result that
a small proportion of a red sediment remains, which possesses all the
characters of the red clay."

       *       *       *       *       *

"It seems evident from the observations here recorded, that _clay_, which
we have hitherto looked upon as essentially the product of the
disintegration of older rocks, may be, under certain circumstances, an
organic formation like chalk; that, as a matter of fact, an area on the
surface of the globe, which we have shown to be of vast extent, although
we are still far from having ascertained its limits, is being covered by
such a deposit at the present day.

"It is impossible to avoid associating such a formation with the fine,
smooth, homogeneous clays and schists, poor in fossils, but showing worm-
tubes and tracks, and bunches of doubtful branching things, such as
Oldhamia, silicious sponges, and thin-shelled peculiar shrimps. Such
formations, more or less metamorphosed, are very familiar, especially to
the student of palaeozoic geology, and they often attain a vast thickness.
One is inclined, from the great resemblance between them in composition
and in the general character of the included fauna, to suspect that these
may be organic formations, like the modern red clay of the Atlantic and
Southern Sea, accumulations of the insoluble ashes of shelled creatures.

"The dredging in the red clay on the 13th of March was usually rich. The
bag contained examples, those with calcareous shells rather stunted, of
most of the characteristic deep-water groups of the Southern Sea,
including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha,
Pourtalesia_, and one or two _Mollusca_. This is, however, very rarely
the case. Generally the red clay is barren, or contains only a very small
number of forms."

It must be admitted that it is very difficult, at present, to frame any
satisfactory explanation of the mode of origin of this singular deposit
of red clay.

I cannot say that the theory put forward tentatively, and with much
reservation by Professor Thomson, that the calcareous matter is dissolved
out by the relatively fresh water of the deep currents from the Antarctic
regions, appears satisfactory to me. Nor do I see my way to the
acceptance of the suggestion of Dr. Carpenter, that the red clay is the
result of the decomposition of previously-formed greensand. At present
there is no evidence that greensand casts are ever formed at great
depths; nor has it been proved that _Glauconite_ is decomposable by the
agency of water and carbonic acid.

I think it probable that we shall have to wait some time for a sufficient
explanation of the origin of the abyssal red clay, no less than for that
of the sublittoral greensand in the intermediate zone. But the importance
of the establishment of the fact that these various deposits are being
formed in the ocean, at the present day, remains the same; whether its
_rationale_ be understood or not.

For, suppose the globe to be evenly covered with sea, to a depth say of a
thousand fathoms--then, whatever might be the mineral matter composing
the sea-bottom, little or no deposit would be formed upon it, the
abrading and denuding action of water, at such a depth, being exceedingly
slight.

Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceous
plants, such as those which now exist in the deep-sea, to be introduced:
they would be distributed according to the same laws as at present, the
sponges (and possibly some of the _Foraminifera_), covering the bottom,
while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, would
increase and multiply in the surface waters. In accordance with the
existing state of things, the _Radiolaria_ and Diatoms would have a
universal distribution, the latter gathering most thickly in the polar
regions, while the _Foraminifera_ would be largely, if not exclusively,
confined to the intermediate zone; and, as a consequence of this
distribution, a bed of "chalk" would begin to form in the intermediate
zone, while caps of silicious rock would accumulate on the circumpolar
regions.

Suppose, further, that a part of the intermediate area were raised to
within two or three hundred fathoms of the surface--for anything that we
know to the contrary, the change of level might determine the
substitution of greensand for the "chalk"; while, on the other hand, if
part of the same area were depressed to three thousand fathoms, that
change might determine the substitution of a different silicate of
alumina and iron--namely, clay--for the "chalk" that would otherwise be
formed.

If the _Challenger_ hypothesis, that the red clay is the residue left by
dissolved _Foraminiferous_ skeletons, is correct, then all these deposits
alike would be directly, or indirectly, the product of living organisms.
But just as a silicious deposit may be metamorphosed into opal or
quartzite, and chalk into marble, so known metamorphic agencies may
metamorphose clay into schist, clay-slate, slate, gneiss, or even
granite. And thus, by the agency of the lowest and simplest of organisms,
our imaginary globe might be covered with strata, of all the chief kinds
of rock of which the known crust of the earth is composed, of indefinite
thickness and extent.

The bearing of the conclusions which are now either established, or
highly probable, respecting the origin of silicious, calcareous, and
clayey rocks, and their metamorphic derivatives, upon the archaeology of
the earth, the elucidation of which is the ultimate object of the
geologist, is of no small importance.

A hundred years ago the singular insight of Linnaeus enabled him to say
that "fossils are not the children but the parents of rocks,"[9] and the
whole effect of the discoveries made since his time has been to compile a
larger and larger commentary upon this text. It is, at present, a
perfectly tenable hypothesis that all siliceous and calcareous rocks are
either directly, or indirectly, derived from material which has, at one
time or other, formed part of the organized framework of living
organisms. Whether the same generalization may be extended to aluminous
rocks, depends upon the conclusion to be drawn from the facts respecting
the red clay areas brought to light by the _Challenger_. If we accept the
view taken by Wyville Thomson and his colleagues--that the red clay is
the residuum left after the calcareous matter of the _Globigerinoe_ ooze
has been dissolved away--then clay is as much a product of life as
limestone, and all known derivatives of clay may have formed part of
animal bodies.

[Footnote 9: "Petrificata montium calcariorum non filii sed parentes
sunt, cum omnis calx oriatur ab animalibus."--_Systema Naturae_, Ed. xii.,
t. iii., p. 154. It must be recollected that Linnaeus included silex, as
well as limestone, under the name of "calx," and that he would probably
have arranged Diatoms among animals, as part of "chaos." Ehrenberg quotes
another even more pithy passage, which I have not been able to find in
any edition of the _Systema_ accessible to me: "Sic lapides ab
animalibus, nec vice versa. Sic runes saxei non primaevi, sed temporis
filiae."]

So long as the _Globigerinoe_;, actually collected at the surface, have
not been demonstrated to contain the elements of clay, the _Challenger_
hypothesis, as I may term it, must be accepted with reserve and
provisionally, but, at present, I cannot but think that it is more
probable than any other suggestion which has been made.

Accepting it provisionally, we arrive at the remarkable result that all
the chief known constituents of the crust of the earth may have formed
part of living bodies; that they may be the "ash" of protoplasm; that the
"_rupes saxei_" are not only _"temporis,"_ but "_vitae filiae_"; and,
consequently, that the time during which life has been active on the
globe may be indefinitely greater than the period, the commencement of
which is marked by the oldest known rocks, whether fossiliferous or
unfossiliferous.

And thus we are led to see where the solution of a great problem and
apparent paradox of geology may lie. Satisfactory evidence now exists
that some animals in the existing world have been derived by a process of
gradual modification from pre-existing forms. It is undeniable, for
example, that the evidence in favour of the derivation of the horse from
the later tertiary _Hipparion_, and that of the _Hipparion_ from
_Anchitherium_, is as complete and cogent as such evidence can reasonably
be expected to be; and the further investigations into the history of the
tertiary mammalia are pushed, the greater is the accumulation of evidence
having the same tendency. So far from palaeontology lending no support to
the doctrine of evolution--as one sees constantly asserted--that
doctrine, if it had no other support, would have been irresistibly forced
upon us by the palaeontological discoveries of the last twenty years.

If, however, the diverse forms of life which now exist have been produced
by the modification of previously-existing less divergent forms, the
recent and extinct species, taken as a whole, must fall into series which
must converge as we go back in time. Hence, if the period represented by
the rocks is greater than, or co-extensive with, that during which life
has existed, we ought, somewhere among the ancient formations, to arrive
at the point to which all these series converge, or from which, in other
words, they have diverged--the primitive undifferentiated protoplasmic
living things, whence the two great series of plants and animals have
taken their departure.

But, as a matter of fact, the amount of convergence of series, in
relation to the time occupied by the deposition of geological formations,
is extraordinarily small. Of all animals the higher _Vertebrata_ are the
most complex; and among these the carnivores and hoofed animals
(_Ungulata_) are highly differentiated. Nevertheless, although the
different lines of modification of the _Carnivora_ and those of the
_Ungulata_, respectively, approach one another, and, although each group
is represented by less differentiated forms in the older tertiary rocks
than at the present day, the oldest tertiary rocks do not bring us near
the primitive form of either. If, in the same way, the convergence of the
varied forms of reptiles is measured against the time during which their
remains are preserved--which is represented by the whole of the tertiary
and mesozoic formations--the amount of that convergence is far smaller
than that of the lines of mammals between the present time and the
beginning of the tertiary epoch. And it is a broad fact that, the lower
we go in the scale of organization, the fewer signs are there of
convergence towards the primitive form from whence all must have
diverged, if evolution be a fact. Nevertheless, that it is a fact in some
cases, is proved, and I, for one, have not the courage to suppose that
the mode in which some species have taken their origin is different from
that in which the rest have originated.

What, then, has become of all the marine animals which, on the hypothesis
of evolution, must have existed in myriads in those seas, wherein the
many thousand feet of Cambrian and Laurentian rocks now devoid, or almost
devoid, of any trace of life were deposited?

Sir Charles Lyell long ago suggested that the azoic character of these
ancient formations might be due to the fact that they had undergone
extensive metamorphosis; and readers of the "Principles of Geology" will
be familiar with the ingenious manner in which he contrasts the theory of
the Gnome, who is acquainted only with the interior of the earth, with
those of ordinary philosophers, who know only its exterior.

The metamorphism contemplated by the great modern champion of rational
geology is, mainly, that brought about by the exposure of rocks to
subterranean heat; and where no such heat could be shown to have
operated, his opponents assumed that no metamorphosis could have taken
place. But the formation of greensand, and still more that of the "red
clay" (if the _Challenger_ hypothesis be correct) affords an insight into
a new kind of metamorphosis--not igneous, but aqueous--by which the
primitive nature of a deposit may be masked as completely as it can be by
the agency of heat. And, as Wyville Thomson suggests, in the passage I
have quoted above (p. 17), it further enables us to assign a new cause
for the occurrence, so puzzling hitherto, of thousands of feet of
unfossiliferous fine-grained schists and slates, in the midst of
formations deposited in seas which certainly abounded in life. If the
great deposit of "red clay" now forming in the eastern valley of the
Atlantic were metamorphosed into slate and then upheaved, it would
constitute an "azoic" rock of enormous extent. And yet that rock is now
forming in the midst of a sea which swarms with living beings, the great
majority of which are provided with calcareous or silicious shells and
skeletons; and, therefore, are such as, up to this time, we should have
termed eminently preservable.

Thus the discoveries made by the _Challenger_ expedition, like all recent
advances in our knowledge of the phenomena of biology, or of the changes
now being effected in the structure of the surface of the earth, are in
accordance with and lend strong support to, that doctrine of
Uniformitarianism, which, fifty years ago, was held only by a small
minority of English geologists--Lyell, Scrope, and De la Beche--but now,
thanks to the long-continued labours of the first two, and mainly to
those of Sir Charles Lyell, has gradually passed from the position of a
heresy to that of catholic doctrine.

Applied within the limits of the time registered by the known fraction of
the crust of the earth, I believe that uniformitarianism is unassailable.
The evidence that, in the enormous lapse of time between the deposition
of the lowest Laurentian strata and the present day, the forces which
have modified the surface of the crust of the earth were different in
kind, or greater in the intensity of their action, than those which are
now occupied in the same work, has yet to be produced. Such evidence as
we possess all tends in the contrary direction, and is in favour of the
same slow and gradual changes occurring then as now.

But this conclusion in nowise conflicts with the deductions of the
physicist from his no less clear and certain data. It may be certain that
this globe has cooled down from a condition in which life could not have
existed; it may be certain that, in so cooling, its contracting crust
must have undergone sudden convulsions, which were to our earthquakes as
an earthquake is to the vibration caused by the periodical eruption of a
Geyser; but in that case, the earth must, like other respectable parents,
have sowed her wild oats, and got through her turbulent youth, before we,
her children, have any knowledge of her.

So far as the evidence afforded by the superficial crust of the earth
goes, the modern geologist can, _ex animo_, repeat the saying of Hutton,
"We find no vestige of a beginning--no prospect of an end." However, he
will add, with Hutton, "But in thus tracing back the natural operations
which have succeeded each other, and mark to us the course of time past,
we come to a period in which we cannot see any further." And if he seek
to peer into the darkness of this period, he will welcome the light
proffered by physics and mathematics.



IV


YEAST

[1871]

It has been known, from time immemorial, that the sweet liquids which may
be obtained by expressing the juices of the fruits and stems of various
plants, or by steeping malted barley in hot water, or by mixing honey
with water--are liable to undergo a series of very singular changes, if
freely exposed to the air and left to themselves, in warm weather.
However clear and pellucid the liquid may have been when first prepared,
however carefully it may have been freed, by straining and filtration,
from even the finest visible impurities, it will not remain clear. After
a time it will become cloudy and turbid; little bubbles will be seen
rising to the surface, and their abundance will increase until the liquid
hisses as if it were simmering on the fire. By degrees, some of the solid
particles which produce the turbidity of the liquid collect at its
surface into a scum, which is blown up by the emerging air-bubbles into a
thick, foamy froth. Another moiety sinks to the bottom, and accumulates
as a muddy sediment, or "lees."

When this action has continued, with more or less violence, for a certain
time, it gradually moderates. The evolution of bubbles slackens, and
finally comes to an end; scum and lees alike settle at the bottom, and
the fluid is once more clear and transparent. But it has acquired
properties of which no trace existed in the original liquid. Instead of
being a mere sweet fluid, mainly composed of sugar and water, the sugar
has more or less completely disappeared; and it has acquired that
peculiar smell and taste which we call "spirituous." Instead of being
devoid of any obvious effect upon the animal economy, it has become
possessed of a very wonderful influence on the nervous system; so that in
small doses it exhilarates, while in larger it stupefies, and may even
destroy life.

Moreover, if the original fluid is put into a still, and heated
moderately, the first and last product of its distillation is simple
water; while, when the altered fluid is subjected to the same process,
the matter which is first condensed in the receiver is found to be a
clear, volatile substance, which is lighter than water, has a pungent
taste and smell, possesses the intoxicating powers of the fluid in an
eminent degree, and takes fire the moment it is brought in contact with a
flame. The Alchemists called this volatile liquid, which they obtained
from wine, "spirits of wine," just as they called hydrochloric acid
"spirits of salt," and as we, to this day, call refined turpentine
"spirits of turpentine." As the "spiritus," or breath, of a man was
thought to be the most refined and subtle part of him, the intelligent
essence of man was also conceived as a sort of breath, or spirit; and, by
analogy, the most refined essence of anything was called its "spirit."
And thus it has come about that we use the same word for the soul of man
and for a glass of gin.

At the present day, however, we even more commonly use another name for
this peculiar liquid--namely, "alcohol," and its origin is not less
singular. The Dutch physician, Van Helmont, lived in the latter part of
the sixteenth and the beginning of the seventeenth century--in the
transition period between alchemy and chemistry--and was rather more
alchemist than chemist. Appended to his "Opera Omnia," published in 1707,
there is a very needful "Clavis ad obscuriorum sensum referendum," in
which the following passage occurs.--

"ALCOHOL.--Chymicis est liquor aut pulvis summe subtilisatus, vocabulo
Orientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_
speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat
... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorum
cancri summe subtilisatus _alcohol_ audit, haud aliter ac spiritus
rectificatissimi _alcolisati_ dicuntur."

Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, so
late as the middle of the last century, the English lexicographer, Nathan
Bailey, defines "alcohol" as "the pure substance of anything separated
from the more gross, a very fine and impalpable powder, or a very pure,
well-rectified spirit." But, by the time of the publication of
Lavoisier's "Traite Elementaire de Chimie," in 1789, the term "alcohol,"
"alkohol," or "alkool" (for it is spelt in all three ways), which Van
Helmont had applied primarily to a fine powder, and only secondarily to
spirits of wine, had lost its primary meaning altogether; and, from the
end of the last century until now, it has, I believe, been used
exclusively as the denotation of spirits of wine, and bodies chemically
allied to that substance.

The process which gives rise to alcohol in a saccharine fluid is known
tones as "fermentation"; a term based upon the apparent boiling up or
"effervescence" of the fermenting liquid, and of Latin origin.

Our Teutonic cousins call the same process "gaehren," "gaesen," "goeschen,"
and "gischen"; but, oddly enough, we do not seem to have retained their
verb or their substantive denoting the action itself, though we do use
names identical with, or plainly derived from, theirs for the scum and
lees. These are called, in Low German, "gaescht" and "gischt"; in Anglo-
Saxon, "gest," "gist," and "yst," whence our "yeast." Again, in Low
German and in Anglo-Saxon there is another name for yeast, having the
form "barm," or "beorm"; and, in the Midland Counties, "barm" is the name
by which yeast is still best known. In High German, there is a third name
for yeast, "hefe," which is not represented in English, so far as I know.

All these words are said by philologers to be derived from roots
expressive of the intestine motion of a fermenting substance. Thus "hefe"
is derived from "heben," to raise; "barm" from "beren" or "baeren," to
bear up; "yeast," "yst," and "gist," have all to do with seething and
foam, with "yeasty" waves, and "gusty" breezes.

The same reference to the swelling up of the fermenting substance is seen
in the Gallo-Latin terms "levure" and "leaven."

It is highly creditable to the ingenuity of our ancestors that the
peculiar property of fermented liquids, in virtue of which they "make
glad the heart of man," seems to have been known in the remotest periods
of which we have any record. All savages take to alcoholic fluids as if
they were to the manner born. Our Vedic forefathers intoxicated
themselves with the juice of the "soma"; Noah, by a not unnatural
reaction against a superfluity of water, appears to have taken the
earliest practicable opportunity of qualifying that which he was obliged
to drink; and the ghosts of the ancient Egyptians were solaced by
pictures of banquets in which the wine-cup passes round, graven on the
walls of their tombs. A knowledge of the process of fermentation,
therefore, was in all probability possessed by the prehistoric
populations of the globe; and it must have become a matter of great
interest even to primaeval wine-bibbers to study the methods by which
fermented liquids could be surely manufactured. No doubt it was soon
discovered that the most certain, as well as the most expeditious, way of
making a sweet juice ferment was to add to it a little of the scum, or
lees, of another fermenting juice. And it can hardly be questioned that
this singular excitation of fermentation in one fluid, by a sort of
infection, or inoculation, of a little ferment taken from some other
fluid, together with the strange swelling, foaming, and hissing of the
fermented substance, must have always attracted attention from the more
thoughtful. Nevertheless, the commencement of the scientific analysis of
the phenomena dates from a period not earlier than the first half of the
seventeenth century.

At this time, Van Helmont made a first step, by pointing out that the
peculiar hissing and bubbling of a fermented liquid is due, not to the
evolution of common air (which he, as the inventor of the term "gas,"
calls "gas ventosum"), but to that of a peculiar kind of air such as is
occasionally met with in caves, mines, and wells, and which he calls "gas
sylvestre."

But a century elapsed before the nature of this "gas sylvestre," or, as
it was afterwards called, "fixed air," was clearly determined, and it was
found to be identical with that deadly "choke-damp" by which the lives of
those who descend into old wells, or mines, or brewers' vats, are
sometimes suddenly ended; and with the poisonous aeriform fluid which is
produced by the combustion of charcoal, and now goes by the name of
carbonic acid gas.

During the same time it gradually became evident that the presence of
sugar was essential to the production of alcohol and the evolution of
carbonic acid gas, which are the two great and conspicuous products of
fermentation. And finally, in 1787, the Italian chemist, Fabroni, made
the capital discovery that the yeast ferment, the presence of which is
necessary to fermentation, is what he termed a "vegeto-animal" substance;
that is, a body which gives of ammoniacal salts when it is burned, and
is, in other ways, similar to the gluten of plants and the albumen and
casein of animals.

These discoveries prepared the way for the illustrious Frenchman,
Lavoisier, who first approached the problem of fermentation with a
complete conception of the nature of the work to be done. The words in
which he expresses this conception, in the treatise on elementary
chemistry to which reference has already been made, mark the year 1789 as
the commencement of a revolution of not less moment in the world of
science than that which simultaneously burst over the political world,
and soon engulfed Lavoisier himself in one of its mad eddies.

"We may lay it down as an incontestable axiom that, in all the operations
of art and nature, nothing is created; an equal quantity of matter exists
both before, and after the experiment: the quality and quantity of the
elements remain precisely the same, and nothing takes place beyond
changes and modifications in the combinations of these elements. Upon
this principle the whole art of performing chemical experiments depends;
we must always suppose an exact equality between the elements of the body
examined and those of the products of its analysis.

"Hence, since from must of grapes we procure alcohol and carbonic acid, I
have an undoubted right to suppose that must consists of carbonic acid
and alcohol. From these premisses we have two modes of ascertaining what
passes during vinous fermentation: either by determining the nature of,
and the elements which compose, the fermentable substances; or by
accurately examining the products resulting from fermentation; and it is
evident that the knowledge of either of these must lead to accurate
conclusions concerning the nature and composition of the other. From
these considerations it became necessary accurately to determine the
constituent elements of the fermentable substances; and for this purpose
I did not make use of the compound juices of fruits, the rigorous
analysis of which is perhaps impossible, but made choice of sugar, which
is easily analysed, and the nature of which I have already explained.
This substance is a true vegetable oxyd, with two bases, composed of
hydrogen and carbon, brought to the state of an oxyd by means of a
certain proportion of oxygen; and these three elements are combined in
such a way that a very slight force is sufficient to destroy the
equilibrium of their connection."

After giving the details of his analysis of sugar and of the products of
fermentation, Lavoisier continues:--

"The effect of the vinous fermentation upon sugar is thus reduced to the
mere separation of its elements into two portions; one part is oxygenated
at the expense of the other, so as to form carbonic acid; while the other
part, being disoxygenated in favour of the latter, is converted into the
combustible substance called alkohol; therefore, if it were possible to
re-unite alkohol and carbonic acid together, we ought to form sugar."[1]

[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated by
Robert Kerr. Second Edition, 1793 (pp. 186-196).]

Thus Lavoisier thought he had demonstrated that the carbonic acid and the
alcohol which are produced by the process of fermentation, are equal in
weight to the sugar which disappears; but the application of the more
refined methods of modern chemistry to the investigation of the products
of fermentation by Pasteur, in 1860, proved that this is not exactly
true, and that there is a deficit of from 5 to 7 per cent of the sugar
which is not covered by the alcohol and carbonic acid evolved. The
greater part of this deficit is accounted for by the discovery of two
substances, glycerine and succinic acid, of the existence of which
Lavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent.
still remains to be made good. According to Pasteur, it has been
appropriated by the yeast, but the fact that such appropriation takes
place cannot be said to be actually proved.

However this may be, there can be no doubt that the constituent elements
of fully 98 per cent. of the sugar which has vanished during fermentation
have simply undergone rearrangement; like the soldiers of a brigade, who
at the word of command divide themselves into the independent regiments
to which they belong. The brigade is sugar, the regiments are carbonic
acid, succinic acid, alcohol, and glycerine.

From the time of Fabroni, onwards, it has been admitted that the agent by
which this surprising rearrangement of the particles of the sugar is
effected is the yeast. But the first thoroughly conclusive evidence of
the necessity of yeast for the fermentation of sugar was furnished by
Appert, whose method of preserving perishable articles of food excited so
much attention in France at the beginning of this century. Gay-Lussac, in
his "Memoire sur la Fermentation,"[2] alludes to Appert's method of
preserving beer-wort unfermented for an indefinite time, by simply
boiling the wort and closing the vessel in which the boiling fluid is
contained, in such a way as thoroughly to exclude air; and he shows that,
if a little yeast be introduced into such wort, after it has cooled, the
wort at once begins to ferment, even though every precaution be taken to
exclude air. And this statement has since received full confirmation from
Pasteur.

[Footnote 2: _Annales de Chimie_, 1810.]

On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amply
proved that air may be allowed to have free access to beer-wort, without
exciting fermentation, if only efficient precautions are taken to prevent
the entry of particles of yeast along with the air.

Thus, the truth that the fermentation of a simple solution of sugar in
water depends upon the presence of yeast, rests upon an unassailable
foundation; and the inquiry into the exact nature of the substance which
possesses such a wonderful chemical influence becomes profoundly
interesting.

The first step towards the solution of this problem was made two
centuries ago by the patient and painstaking Dutch naturalist,
Leeuwenhoek, who in the year 1680 wrote thus:--

"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis per
materiam pellucidam fluitantibus, quarm cerevisiam esse censui, constare
observavi: vidi etiam evidentissime, unumquemque hujus fermenti globulum
denuo ex sex distinctis globulis constare, accurate eidem quantitate et
formae, cui globulis sanguinis nostri, respondentibus.

"Verum talis mihi de horum origine et formatione conceptus formabam;
globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se
constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam
cerevisiam vocare licet, refrigescente, multos ex minimis particulis in
cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae
sexta pars est globuli faecis, et iterum sex ex hisce globulis
conjungi."[3]

[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.]

Thus Leeuwenhoek discovered that yeast consists of globules floating in a
fluid; but he thought that they were merely the starchy particles of the
grain from which the wort was made, rearranged. He discovered the fact
that yeast had a definite structure, but not the meaning of the fact. A
century and a half elapsed, and the investigation of yeast was
recommenced almost simultaneously by Cagniard de la Tour in France, and
by Schwann and Kuetzing in Germany. The French observer was the first to
publish his results; and the subject received at his hands and at those
of his colleague, the botanist Turpin, full and satisfactory
investigation.

The main conclusions at which they arrived are these. The globular, or
oval, corpuscles which float so thickly in the yeast as to make it muddy,
though the largest are not more than one two-thousandth of an inch in
diameter, and the smallest may measure less than one seven-thousandth of
an inch, are living organisms. They multiply with great rapidity by
giving off minute buds, which soon attain the size of their parent, and
then either become detached or remain united, forming the compound
globules of which Leeuwenhoek speaks, though the constancy of their
arrangement in sixes existed only in the worthy Dutchman's imagination.

It was very soon made out that these yeast organisms, to which Turpin
gave the name of _Torula cerevisioe_, were more nearly allied to the
lower Fungi than to anything else. Indeed Turpin, and subsequently
Berkeley and Hoffmann, believed that they had traced the development of
the _Torula_ into the well-known and very common mould--the _Penicillium
glaucum_. Other observers have not succeeded in verifying these
statements; and my own observations lead me to believe, that while the
connection between _Torula_ and the moulds is a very close one, it is of
a different nature from that which has been supposed. I have never been
able to trace the development of _Torula_ into a true mould; but it is
quite easy to prove that species of true mould, such as _Penicillium_,
when sown in an appropriate nidus, such as a solution of tartrate of
ammonia and yeast-ash, in water, with or without sugar, give rise to
_Toruloe_, similar in all respects to _T. cerevisioe_, except that they
are, on the average, smaller. Moreover, Bail has observed the development
of a _Torula_ larger than _T. cerevisioe_, from a _Mucor_, a mould allied
to _Penicillium_.

It follows, therefore, that the _Toruloe_, or organisms of yeast, are
veritable plants; and conclusive experiments have proved that the power
which causes the rearrangement of the molecules of the sugar is
intimately connected with the life and growth of the plant. In fact,
whatever arrests the vital activity of the plant also prevents it from
exciting fermentation.

Such being the facts with regard to the nature of yeast, and the changes
which it effects in sugar, how are they to be accounted for? Before
modern chemistry had come into existence, Stahl, stumbling, with the
stride of genius, upon the conception which lies at the bottom of all
modern views of the process, put forward the notion that the ferment,
being in a state of internal motion, communicated that motion to the
sugar, and thus caused its resolution into new substances. And Lavoisier,
as we have seen, adopts substantially the same view. But Fabroni, full of
the then novel conception of acids and bases and double decompositions,
propounded the hypothesis that sugar is an oxide with two bases, and the
ferment a carbonate with two bases; that the carbon of the ferment unites
with the oxygen of the sugar, and gives rise to carbonic acid; while the
sugar, uniting with the nitrogen of the ferment, produces a new substance
analogous to opium. This is decomposed by distillation, and gives rise to
alcohol. Next, in 1803, Thenard propounded a hypothesis which partakes
somewhat of the nature of both Stahl's and Fabroni's views. "I do not
believe with Lavoisier," he says, "that all the carbonic acid formed
proceeds from the sugar. How, in that case, could we conceive the action
of the ferment on it? I think that the first portions of the acid are due
to a combination of the carbon of the ferment with the oxygen of the
sugar, and that it is by carrying off a portion of oxygen from the last
that the ferment causes the fermentation to commence--the equilibrium
between the principles of the sugar being disturbed, they combine afresh
to form carbonic acid and alcohol."

The three views here before us may be familiarly exemplified by supposing
the sugar to be a card-house. According to Stahl, the ferment is somebody
who knocks the table, and shakes the card-house down; according to
Fabroni, the ferment takes out some cards, but puts others in their
places; according to Thenard, the ferment simply takes a card out of the
bottom story, the result of which is that all the others fall.

As chemistry advanced, facts came to light which put a new face upon
Stahl's hypothesis, and gave it a safer foundation than it previously
possessed. The general nature of these phenomena may be thus stated:--A
body, A, without giving to, or taking from, another body B, any material
particles, causes B to decompose into other substances, C, D, E, the sum
of the weights of which is equal to the weight of B, which decomposes.
Thus, bitter almonds contain two substances, amygdalin and synaptase,
which can be extracted, in a separate state, from the bitter almonds. The
amygdalin thus obtained, if dissolved in water, undergoes no change; but
if a little synaptase be added to the solution, the amygdalin splits up
into bitter almond oil, prussic acid, and a kind of sugar.

A short time after Cagniard de la Tour discovered the yeast plant,
Liebig, struck with the similarity between this and other such processes
and the fermentation of sugar, put forward the hypothesis that yeast
contains a substance which acts upon sugar, as synaptase acts upon
amygdalin. And as the synaptase is certainly neither organized nor alive,
but a mere chemical substance, Liebig treated Cagniard de la Tour's
discovery with no small contempt, and, from that time to the present, has
steadily repudiated the notion that the decomposition of the sugar is, in
any sense, the result of the vital activity of the _Torula_. But, though
the notion that the _Torula_ is a creature which eats sugar and excretes
carbonic acid and alcohol, which is not unjustly ridiculed in the most
surprising paper that ever made its appearance in a grave scientific
journal,[4] may be untenable, the fact that the _Toruloe_ are alive, and
that yeast does not excite fermentation unless it contains living
_Toruloe_, stands fast. Moreover, of late years, the essential
participation of living organisms in fermentation other than the
alcoholic, has been clearly made out by Pasteur and other chemists.

[Footnote 4: "Das entraethselte Geheimniss der geistigen Gaehrung
(Vorlaenfige briefliche Mittheilung)" is the title of an anonymous
contribution to Woehler and Liebig's _Annalen der Pharmacie_ for 1839, in
which a somewhat Rabelaisian imaginary description of the organisation of
the "yeast animals" and of the manner in which their functions are
performed, is given with a circumstantiality worthy of the author of
_Gulliver's Travels_. As a specimen of the writer's humour, his account
of what happens when fermentation comes to an end may suffice. "Sobald
naemlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich
gegenseitig selbst auf, was durch eine eigene Manipulation geschieht;
alles wird verdant bis auf die Eier, welche unveraendert durch den
Darmkanal hineingehen; man hat zuletzt wieder gaehrungsfaehige Hefe,
naemlich den Saamen der Thiere, der uebrig bleibt."] However, it may be
asked, is there any necessary opposition between the so-called "vital"
and the strictly physico-chemical views of fermentation? It is quite
possible that the living _Torula_ may excite fermentation in sugar,
because it constantly produces, as an essential part of its vital
manifestations, some substance which acts upon the sugar, just as the
synaptase acts upon the amygdalin. Or it may be, that, without the
formation of any such special substance, the physical condition of the
living tissue of the yeast plant is sufficient to effect that small
disturbance of the equilibrium of the particles of the sugar, which
Lavoisier thought sufficient to effect its decomposition.

Platinum in a very fine state of division--known as platinum black, or
_noir de platine_--has the very singular property of causing alcohol to
change into acetic acid with great rapidity. The vinegar plant, which is
closely allied to the yeast plant, has a similar effect upon dilute
alcohol, causing it to absorb the oxygen of the air, and become converted
into vinegar; and Liebig's eminent opponent, Pasteur, who has done so
much for the theory and the practice of vinegar-making, himself suggests
that in this case--

"La cause du phenomene physique qui accompagne la vie de la plante reside
dans un etat physique propre, analogue a celui du noir de platine. Mais
il est essentiel de remarquer que cet etat physique de la plante est
etroitement lie avec la vie de cette plante."[5]

[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.]

Now, if the vinegar plant gives rise to the oxidation of alcohol, on
account of its merely physical constitution, it is at any rate possible
that the physical constitution of the yeast plant may exert a decomposing
influence on sugar.

But, without presuming to discuss a question which leads us into the very
arcana of chemistry, the present state of speculation upon the _modus
operandi_ of the yeast plant in producing fermentation is represented, on
the one hand, by the Stahlian doctrine, supported by Liebig, according to
which the atoms of the sugar are shaken into new combinations either
directly by the _Toruloe_, or indirectly, by some substance formed by
them; and, on the other hand, by the Thenardian doctrine, supported by
Pasteur, according to which the yeast plant assimilates part of the
sugar, and, in so doing, disturbs the rest, and determines its resolution
into the products of fermentation. Perhaps the two views are not so much
opposed as they seem at first sight to be.

But the interest which attaches to the influence of the yeast plants upon
the medium in which they live and grow does not arise solely from its
bearing upon the theory of fermentation. So long ago as 1838, Turpin
compared the _Toruloe_ to the ultimate elements of the tissues of animals
and plants--"Les organes elementaires de leurs tissus, comparables aux
petits vegetaux des levures ordinaires, sont aussi les decompositeurs des
substances qui les environnent."

Almost at the same time, and, probably, equally guided by his study of
yeast, Schwann was engaged in those remarkable investigations into the
form and development of the ultimate structural elements of the tissues
of animals, which led him to recognise their fundamental identity with
the ultimate structural elements of vegetable organisms.

The yeast plant is a mere sac, or "cell," containing a semi-fluid matter,
and Schwann's microscopic analysis resolved all living organisms, in the
long run, into an aggregation of such sacs or cells, variously modified;
and tended to show, that all, whatever their ultimate complication, begin
their existence in the condition of such simple cells.

In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_
as a "cell"; and, in a remarkable note to the passage in which he refers
to the yeast plant, Schwann says:--

"I have been unable to avoid mentioning fermentation, because it is the
most fully and exactly known operation of cells, and represents, in the
simplest fashion, the process which is repeated by every cell of the
living body."

In other words, Schwann conceives that every cell of the living body
exerts an influence on the matter which surrounds and permeates it,
analogous to that which a _Torula_ exerts on the saccharine solution by
which it is bathed. A wonderfully suggestive thought, opening up views of
the nature of the chemical processes of the living body, which have
hardly yet received all the development of which they are capable.

Kant defined the special peculiarity of the living body to be that the
parts exist for the sake of the whole and the whole for the sake of the
parts. But when Turpin and Schwann resolved the living body into an
aggregation of quasi-independent cells, each, like a _Torula_, leading
its own life and having its own laws of growth and development, the
aggregation being dominated and kept working towards a definite end only
by a certain harmony among these units, or by the superaddition of a
controlling apparatus, such as a nervous system, this conception ceased
to be tenable. The cell lives for its own sake, as well as for the sake
of the whole organism; and the cells which float in the blood, live at
its expense, and profoundly modify it, are almost as much independent
organisms as the _Toruloe_ which float in beer-wort.

Schwann burdened his enunciation of the "cell theory" with two false
suppositions; the one, that the structures he called "nucleus"[6] and
"cell-wall" are essential to a cell; the other, that cells are usually
formed independently of other cells; but, in 1839, it was a vast and
clear gain to arrive at the conception, that the vital functions of all
the higher animals and plants are the resultant of the forces inherent in
the innumerable minute cells of which they are composed, and that each of
them is, itself, an equivalent of one of the lowest and simplest of
independent living beings--the _Torula_.

[Footnote 6: Later investigations have thrown an entirely new light upon
the structure and the functional importance of the nucleus; and have
proved that Schwann did not over-estimate its importance. 1894.]

From purely morphological investigations, Turpin and Schwann, as we have
seen, arrived at the notion of the fundamental unity of structure of
living beings. And, before long, the researches of chemists gradually led
up to the conception of the fundamental unity of their composition.

So far back as 1803, Thenard pointed out, in most distinct terms, the
important fact that yeast contains a nitrogenous "animal" substance; and
that such a substance is contained in all ferments. Before him, Fabroni
and Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulder
endeavoured to demonstrate that a peculiar substance, which he called
"protein," was essentially characteristic of living matter.

In 1846, Payen writes:--

"Enfin, une loi sans exception me semble apparaitre dans les faits
nombreux que j'ai observes et conduire a envisager sous un nouveau jour
la vie vegetale; si je ne m'abuse, tout ce que dans les tissus vegetaux
la vue directe ou amplifiee nous permet de discerner sous la forme de
cellules et de vaisseaux, ne represente autre chose que les enveloppes
protectrices, les reservoirs et les conduits, a l'aide desquels les corps
animes qui les secretent et les faconnent, se logent, puisent et
charrient leurs aliments, deposent et isolent les matieres excretees."

And again:--

"Afin de completer aujourd'hui l'enonce du fait general, je rappellerai
que les corps, doue des fonctions accomplies dans les tissus des plantes,
sont formes des elements qui constituent, en proportion peu variable, les
organismes animaux; qu'ainsi l'on est conduit a reconnaitre une immense
unite de composition elementaire dans tous les corps vivants de la
nature."[7]

[Footnote 7: Mem. sur les Developpements des Vegetaux, &c.--_Mem.
Presentees_. ix. 1846.]

In the year (1846) in which these remarkable passages were published, the
eminent German botanist, Von Mohl invented the word "protoplasm," as a
name for one portion of those nitrogenous contents of the cells of living
plants, the close chemical resemblance of which to the essential
constituents of living animals is so strongly indicated by Payen. And
through the twenty-five years that have passed, since the matter of life
was first called protoplasm, a host of investigators, among whom Cohn,
Max Schulze, and Kuehne must be named as leaders, have accumulated
evidence, morphological, physiological, and chemical, in favour of that
"immense unite de composition elementaire dans tous les corps vivants de
la nature," into which Payen had, so early, a clear insight.

As far back as 1850, Cohn wrote, apparently without any knowledge of what
Payen had said before him:--

"The protoplasm of the botanist, and the contractile substance and
sarcode of the zoologist, must be, if not identical, yet in a high degree
analogous substances. Hence, from this point of view, the difference
between animals and plants consists in this; that, in the latter, the
contractile substance, as a primordial utricle, is enclosed within an
inert cellulose membrane, which permits it only to exhibit an internal
motion, expressed by the phenomena of rotation and circulation, while, in
the former, it is not so enclosed. The protoplasm in the form of the
primordial utricle is, as it were, the animal element in the plant, but
which is imprisoned, and only becomes free in the animal; or, to strip
off the metaphor which obscures simple thought, the energy of organic
vitality which is manifested in movement is especially exhibited by a
nitrogenous contractile substance, which in plants is limited and
fettered by an inert membrane, in animals not so."[8]

[Footnote 8: Cohn, "Ueber Protococcus pluvialis," in the _Nova Acta_ for
1850.]

In 1868, thinking that an untechnical statement of the views current
among the leaders of biological science might be interesting to the
general public, I gave a lecture embodying them in Edinburgh. Those who
have not made the mistake of attempting to approach biology, either by
the high _a priori_ road of mere philosophical speculation, or by the
mere low _a posteriori_ lane offered by the tube of a microscope, but
have taken the trouble to become acquainted with well-ascertained facts
and with their history, will not need to be told that in what I had to
say "as regards protoplasm" in my lecture "On the Physical Basis of Life"
(Vol. I. of these Essays, p. 130), there was nothing new; and, as I hope,
nothing that the present state of knowledge does not justify us in
believing to be true. Under these circumstances, my surprise may be
imagined, when I found, that the mere statement of facts and of views,
long familiar to me as part of the common scientific property of
Continental workers, raised a sort of storm in this country, not only by
exciting the wrath of unscientific persons whose pet prejudices they
seemed to touch, but by giving rise to quite superfluous explosions on
the part of some who should have been better informed.

Dr. Stirling, for example, made my essay the subject of a special
critical lecture,[9] which I have read with much interest, though, I
confess, the meaning of much of it remains as dark to me as does the
"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr.
Stirling's method of dealing with the subject is peculiar. "Protoplasm"
is a question of history, so far as it is a name; of fact, so far as it
is a thing. Dr. Stirling, has not taken the trouble to refer to the
original authorities for his history, which is consequently a travesty;
and still less has he concerned himself with looking at the facts, but
contents himself with taking them also at second-hand. A most amusing
example of this fashion of dealing with scientific statements is
furnished by Dr. Stirling's remarks upon my account of the protoplasm of
the nettle hair. That account was drawn up from careful and often-
repeated observation of the facts. Dr. Stirling thinks he is offering a
valid criticism, when he says that my valued friend Professor Stricker
gives a somewhat different statement about protoplasm. But why in the
world did not this distinguished Hegelian look at a nettle hair for
himself, before venturing to speak about the matter at all? Why trouble
himself about what either Stricker or I say, when any tyro can see the
facts for himself, if he is provided with those not rare articles, a
nettle and a microscope? But I suppose this would have been
"_Aufklaerung_"--a recurrence to the base common-sense philosophy of the
eighteenth century, which liked to see before it believed, and to
understand before it criticised Dr. Stirling winds up his paper with the
following paragraph:--

[Footnote 9: Subsequently published under the title of "As regards
Protoplasm."]

"In short, the whole position of Mr. Huxley, (1) that all organisms
consist alike of the same life-matter, (2) which life-matter is, for its
part, due only to chemistry, must be pronounced untenable--nor less
untenable (3) the materialism he would found on it."

The paragraph contains three distinct assertions concerning my views, and
just the same number of utter misrepresentations of them. That which I
have numbered (1) turns on the ambiguity of the word "same," for a
discussion of which I would refer Dr. Stirling to a great hero of
"_Aufklaerung_" Archbishop Whately; statement number (2) is, in my
judgment, absurd, and certainly I have never said anything resembling it;
while, as to number (3), one great object of my essay was to show that
what is called "materialism" has no sound philosophical basis!

As we have seen, the study of yeast has led investigators face to face
with problems of immense interest in pure chemistry, and in animal and
vegetable morphology. Its physiology is not less rich in subjects for
inquiry. Take, for example, the singular fact that yeast will increase
indefinitely when grown in the dark, in water containing only tartrate of
ammonia a small percentage of mineral salts and sugar. Out of these
materials the _Toruloe_ will manufacture nitrogenous protoplasm,
cellulose, and fatty matters, in any quantity, although they are wholly
deprived of those rays of the sun, the influence of which is essential to
the growth of ordinary plants. There has been a great deal of speculation
lately, as to how the living organisms buried beneath two or three
thousand fathoms of water, and therefore in all probability almost
deprived of light, live. If any of them possess the same powers as yeast
(and the same capacity for living without light is exhibited by some
other fungi) there would seem to be no difficulty about the matter.

Of the pathological bearings of the study of yeast, and other such
organisms, I have spoken elsewhere. It is certain that, in some animals,
devastating epidemics are caused by fungi of low order--similar to those
of which _Torula_ is a sort of offshoot. It is certain that such diseases
are propagated by contagion and infection, in just the same way as
ordinary contagious and infectious diseases are propagated. Of course, it
does not follow from this, that all contagious and infectious diseases
are caused by organisms of as definite and independent a character as the
_Torula_; but, I think, it does follow that it is prudent and wise to
satisfy one's self in each particular case, that the "germ theory" cannot
and will not explain the facts, before having recourse to hypotheses
which have no equal support from analogy.



V


ON THE FORMATION OF COAL

[1870]

The lumps of coal in a coal-scuttle very often have a roughly cubical
form. If one of them be picked out and examined with a little care, it
will be found that its six sides are not exactly alike. Two opposite
sides are comparatively smooth and shining, while the other four are much
rougher, and are marked by lines which run parallel with the smooth
sides. The coal readily splits along these lines, and the split surfaces
thus formed are parallel with the smooth faces. In other words, there is
a sort of rough and incomplete stratification in the lump of coal, as if
it were a book, the leaves of which had stuck together very closely.

Sometimes the faces along which the coal splits are not smooth, but
exhibit a thin layer of dull, charred-looking substance, which is known
as "mineral charcoal."

Occasionally one of the faces of a lump of coal will present impressions,
which are obviously those of the stem, or leaves, of a plant; but though
hard mineral masses of pyrites, and even fine mud, may occur here and
there, neither sand nor pebbles are met with.

When the coal burns, the chief ultimate products of its combustion are
carbonic acid, water, and ammoniacal products, which escape up the
chimney; and a greater or less amount of residual earthy salts, which
take the form of ash. These products are, to a great extent, such as
would result from the burning of so much wood.

These properties of coal may be made out without any very refined
appliances, but the microscope reveals something more. Black and opaque
as ordinary coal is, slices of it become transparent if they are cemented
in Canada balsam, and rubbed down very thin, in the ordinary way of
making thin sections of non-transparent bodies. But as the thin slices,
made in this way, are very apt to crack and break into fragments, it is
better to employ marine glue as the cementing material. By the use of
this substance, slices of considerable size and of extreme thinness and
transparency may be obtained.[1]

[Footnote 1: My assistant in the Museum of Practical Geology, Mr. Newton,
invented this excellent method of obtaining thin slices of coal.]

Now let us suppose two such slices to be prepared from our lump of coal--
one parallel with the bedding, the other perpendicular to it; and let us
call the one the horizontal, and the other the vertical, section. The
horizontal section will present more or less rounded yellow patches and
streaks, scattered irregularly through the dark brown, or blackish,
ground substance; while the vertical section will exhibit mere elongated
bars and granules of the same yellow materials, disposed in lines which
correspond, roughly, with the general direction of the bedding of the
coal.

This is the microscopic structure of an ordinary piece of coal. But if a
great series of coals, from different localities and seams, or even from
different parts of the same seam, be examined, this structure will be
found to vary in two directions. In the anthracitic, or stone-coals,
which burn like coke, the yellow matter diminishes, and the ground
substance becomes more predominant, blacker, and more opaque, until it
becomes impossible to grind a section thin enough to be translucent;
while, on the other hand, in such as the "Better-Bed" coal of the
neighbourhood of Bradford, which burns with much flame, the coal is of a
far lighter, colour and transparent sections are very easily obtained. In
the browner parts of this coal, sharp eyes will readily detect multitudes
of curious little coin-shaped bodies, of a yellowish brown colour,
embedded in the dark brown ground substance. On the average, these little
brown bodies may have a diameter of about one-twentieth of an inch. They
lie with their flat surfaces nearly parallel with the two smooth faces of
the block in which they are contained; and, on one side of each, there
may be discerned a figure, consisting of three straight linear marks,
which radiate from the centre of the disk, but do not quite reach its
circumference. In the horizontal section these disks are often converted
into more or less complete rings; while in the vertical sections they
appear like thick hoops, the sides of which have been pressed together.
The disks are, therefore, flattened bags; and favourable sections show
that the three-rayed marking is the expression of three clefts, which
penetrate one wall of the bag.

The sides of the bags are sometimes closely approximated; but, when the
bags are less flattened, their cavities are, usually, filled with
numerous, irregularly rounded, hollow bodies, having the same kind of
wall as the large ones, but not more than one seven-hundredth of an inch
in diameter.

In favourable specimens, again, almost the whole ground substance appears
to be made up of similar bodies--more or less carbonized or blackened--
and, in these, there can be no doubt that, with the exception of patches
of mineral charcoal, here and there, the whole mass of the coal is made
up of an accumulation of the larger and of the smaller sacs.

But, in one and the same slice, every transition can be observed from
this structure to that which has been described as characteristic of
ordinary coal. The latter appears to rise out of the former, by the
breaking-up and increasing carbonization of the larger and the smaller
sacs. And, in the anthracitic coals, this process appears to have gone to
such a length, as to destroy the original structure altogether, and to
replace it by a completely carbonized substance.

Thus coal may be said, speaking broadly, to be composed of two
constituents: firstly, mineral charcoal; and, secondly, coal proper. The
nature of the mineral charcoal has long since been determined. Its
structure shows it to consist of the remains of the stems and leaves of
plants, reduced a little more than their carbon. Again, some of the coal
is made up of the crushed and flattened bark, or outer coat, of the stems
of plants, the inner wood of which has completely decayed away. But what
I may term the "saccular matter" of the coal, which, either in its
primary or in its degraded form constitutes by far the greater part of
all the bituminous coals I have examined, is certainly not mineral
charcoal; nor is its structure that of any stem or leaf. Hence its real
nature is at first by no means apparent, and has been the subject of much
discussion.

The first person who threw any light upon the problem, as far as I have
been able to discover, was the well-known geologist, Professor Morris. It
is now thirty-four years since he carefully described and figured the
coin-shaped bodies, or larger sacs, as I have called them, in a note
appended to the famous paper "On the Coalbrookdale Coal-Field," published
at that time, by the present President of the Geological Society, Mr.
Prestwich. With much sagacity, Professor Morris divined the real nature
of these bodies, and boldly affirmed them to be the spore-cases of a
plant allied to the living club-mosses.

But discovery sometimes makes a long halt; and it is only a few years
since Mr. Carruthers determined the plant (or rather one of the plants)
which produces these spore-cases, by finding the discoidal sacs still
adherent to the leaves of the fossilized cone which produced them. He
gave the name of _Flemingites gracilis_ to the plant of which the cones
form a part. The branches and stem of this plant are not yet certainly
known, but there is no sort of doubt that it was closely allied to the
_Lepidodendron_, the remains of which abound in the coal formation. The
_Lepidodendra_ were shrubs and trees which put one more in mind of an
_Araucaria_ than of any other familiar plant; and the ends of the
fruiting branches were terminated by cones, or catkins, somewhat like the
bodies so named in a fir, or a willow. These conical fruits, however, did
not produce seeds; but the leaves of which they were composed bore upon
their surfaces sacs full of spores or sporangia, such as those one sees
on the under surface of a bracken leaf. Now, it is these sporangia of the
Lepidodendroid plant _Flemingites_ which were identified by Mr.
Carruthers with the free sporangia described by Professor Morris, which
are the same as the large sacs of which I have spoken. And, more than
this, there is no doubt that the small sacs are the spores, which were
originally contained in the sporangia.

The living club-mosses are, for the most part, insignificant and creeping
herbs, which, superficially, very closely resemble true mosses, and none
of them reach more than two or three feet in height. But, in their
essential structure, they very closely resemble the earliest
Lepidodendroid trees of the coal: their stems and leaves are similar; so
are their cones; and no less like are the sporangia and spores; while
even in their size, the spores of the _Lepidodendron_ and those of the
existing _Lycopodium_, or club-moss, very closely approach one another.

Thus, the singular conclusion is forced upon us, that the greater and the
smaller sacs of the "Better-Bed" and other coals, in which the primitive
structure is well preserved, are simply the sporangia and spores of
certain plants, many of which were closely allied to the existing club-
mosses. And if, as I believe, it can be demonstrated that ordinary coal
is nothing but "saccular" coal which has undergone a certain amount of
that alteration which, if continued, would convert it into anthracite;
then, the conclusion is obvious, that the great mass of the coal we burn
is the result of the accumulation of the spores and spore-cases of
plants, other parts of which have furnished the carbonized stems and the
mineral charcoal, or have left their impressions on the surfaces of the
layer.

Of the multitudinous speculations which, at various times, have been
entertained respecting the origin and mode of formation of coal, several
appear to be negatived, and put out of court, by the structural facts the
significance of which I have endeavoured to explain. These facts, for
example, do not permit us to suppose that coal is an accumulation of
peaty matter, as some have held.

Again, the late Professor Quekett was one of the first observers who gave
a correct description of what I have termed the "saccular" structure of
coal; and, rightly perceiving that this structure was something quite
different from that of any known plant, he imagined that it proceeded
from some extinct vegetable organism which was peculiarly abundant
amongst the coal-forming plants. But this explanation is at once shown to
be untenable when the smaller and the larger sacs are proved to be spores
or sporangia.

Some, once more, have imagined that coal was of submarine origin; and
though the notion is amply and easily refuted by other considerations, it
may be worth while to remark, that it is impossible to comprehend how a
mass of light and resinous spores should have reached the bottom of the
sea, or should have stopped in that position if they had got there.

At the same time, it is proper to remark that I do not presume to suggest
that all coal must needs have the same structure; or that there may not
be coals in which the proportions of wood and spores, or spore-cases, are
very different from those which I have examined. All I repeat is, that
none of the coals which have come under my notice have enabled me to
observe such a difference. But, according to Principal Dawson, who has so
sedulously examined the fossil remains of plants in North America, it is
otherwise with the vast accumulations of coal in that country.

"The true coal," says Dr. Dawson, "consists principally of the flattened
bark of Sigillarioid and other trees, intermixed with leaves of Ferns and
_Cordaites_, and other herbaceous _debris_, and with fragments of decayed
wood, constituting 'mineral charcoal,' all these materials having
manifestly alike grown and accumulated where we find them."[2]

[Footnote 2: _Acadian Geology_, 2nd edition, p. 135.]

When I had the pleasure of seeing Principal Dawson in London last summer,
I showed him my sections of coal, and begged him to re-examine some of
the American coals on his return to Canada, with an eye to the presence
of spores and sporangia, such as I was able to show him in our English
and Scotch coals. He has been good enough to do so; and in a letter dated
September 26th, 1870, he informs me that--

"Indications of spore-cases are rare, except in certain coarse shaly
coals and portions of coals, and in the roofs of the seams. The most
marked case I have yet met with is the shaly coal referred to as
containing _Sporangites_ in my paper on the conditions of accumulation of
coal ("Journal of the Geological Society," vol. xxii. pp. 115, 139, and
165). The purer coals certainly consist principally of cubical tissues
with some true woody matter, and the spore-cases, &c., are chiefly in the
coarse and shaly layers. This is my old doctrine in my two papers in the
"Journal of the Geological Society," and I see nothing to modify it. Your
observations, however, make it probable that the frequent _clear spots_
in the cannels are spore-cases."

Dr. Dawson's results are the more remarkable, as the numerous specimens
of British coal, from various localities, which I have examined, tell one
tale as to the predominance of the spore and sporangium element in their
composition; and as it is exactly in the finest and purest coals, such as
the "Better-Bed" coal of Lowmoor, that the spores and sporangia obviously
constitute almost the entire mass of the deposit.

Coal, such as that which has been described, is always found in sheets,
or "seams," varying from a fraction of an inch to many feet in thickness,
enclosed in the substance of the earth at very various depths, between
beds of rock of different kinds. As a rule, every seam of coal rests upon
a thicker, or thinner, bed of clay, which is known as "under-clay." These
alternations of beds of coal, clay, and rock may be repeated many times,
and are known as the "coal-measures"; and in some regions, as in South
Wales and in Nova Scotia, the coal-measures attain a thickness of twelve
or fourteen thousand feet, and enclose eighty or a hundred seams of coal,
each with its under-clay, and separated from those above and below by
beds of sandstone and shale.

The position of the beds which constitute the coal-measures is infinitely
diverse. Sometimes they are tilted up vertically, sometimes they are
horizontal, sometimes curved into great basins; sometimes they come to
the surface, sometimes they are covered up by thousands of feet of rock.
But, whatever their present position, there is abundant and conclusive
evidence that every under-clay was once a surface soil. Not only do
carbonized root-fibres frequently abound in these under-clays; but the
stools of trees, the trunks of which are broken off and confounded with
the bed of coal, have been repeatedly found passing into radiating roots,
still embedded in the under-clay. On many parts of the coast of England,
what are commonly known as "submarine forests" are to be seen at low
water. They consist, for the most part, of short stools of oak, beech,
and fir-trees, still fixed by their long roots in the bed of blue clay in
which they originally grew. If one of these submarine forest beds should
be gradually depressed and covered up by new deposits, it would present
just the same characters as an under-clay of the coal, if the
_Sigillaria_ and _Lepidodendron_ of the ancient world were substituted
for the oak, or the beech, of our own times.

In a tropical forest, at the present day, the trunks of fallen trees, and
the stools of such trees as may have been broken by the violence of
storms, remain entire for but a short time. Contrary to what might be
expected, the dense wood of the tree decays, and suffers from the ravages
of insects, more swiftly than the bark. And the traveller, setting his
foot on a prostrate trunk, finds that it is a mere shell, which breaks
under his weight, and lands his foot amidst the insects, or the reptiles,
which have sought food or refuge within.

The trees of the coal forests present parallel conditions. When the
fallen trunks which have entered into the composition of the bed of coal
are identifiable, they are mere double shells of bark, flattened together
in consequence of the destruction of the woody core; and Sir Charles
Lyell and Principal Dawson discovered, in the hollow stools of coal trees
of Nova Scotia, the remains of snails, millipedes, and salamander-like
creatures, embedded in a deposit of a different character from that which
surrounded the exterior of the trees. Thus, in endeavouring to comprehend
the formation of a seam of coal, we must try to picture to ourselves a
thick forest, formed for the most part of trees like gigantic club-
mosses, mares'-tails, and tree-ferns, with here and there some that had
more resemblance to our existing yews and fir-trees. We must suppose
that, as the seasons rolled by, the plants grew and developed their
spores and seeds; that they shed these in enormous quantities, which
accumulated on the ground beneath; and that, every now and then, they
added a dead frond or leaf; or, at longer intervals, a rotten branch, or
a dead trunk, to the mass.

A certain proportion of the spores and seeds no doubt fulfilled their
obvious function, and, carried by the wind to unoccupied regions,
extended the limits of the forest; many might be washed away by rain into
streams, and be lost; but a large portion must have remained, to
accumulate like beech-mast, or acorns, beneath the trees of a modern
forest.

But, in this case it may be asked, why does not our English coal consist
of stems and leaves to a much greater extent than it does? What is the
reason of the predominance of the spores and spore-cases in it?

A ready answer to this question is afforded by the study of a living
full-grown club-moss. Shake it upon a piece of paper, and it emits a
cloud of fine dust, which falls over the paper, and is the well-known
Lycopodium powder. Now this powder used to be, and I believe still is,
employed for two objects which seem, at first sight, to have no
particular connection with one another. It is, or was, employed in making
lightning, and in making pills. The coats of the spores contain so much
resinous matter, that a pinch of Lycopodium powder, thrown through the
flame of a candle, burns with an instantaneous flash, which has long done
duty for lightning on the stage. And the same character makes it a
capital coating for pills; for the resinous powder prevents the drug from
being wetted by the saliva, and thus bars the nauseous flavour from the
sensitive papilla; of the tongue.

But this resinous matter, which lies in the walls of the spores and
sporangia, is a substance not easily altered by air and water, and hence
tends to preserve these bodies, just as the bituminized cerecloth
preserves an Egyptian mummy; while, on the other hand, the merely woody
stem and leaves tend to rot, as fast as the wood of the mummy's coffin
has rotted. Thus the mixed heap of spores, leaves, and stems in the coal-
forest would be persistently searched by the long-continued action of air
and rain; the leaves and stems would gradually be reduced to little but
their carbon, or, in other words, to the condition of mineral charcoal in
which we find them; while the spores and sporangia remained as a
comparatively unaltered and compact residuum.

There is, indeed, tolerably clear evidence that the coal must, under some
circumstances, have been converted into a substance hard enough to be
rolled into pebbles, while it yet lay at the surface of the earth; for in
some seams of coal, the courses of rivulets, which must have been living
water, while the stratum in which their remains are found was still at
the surface, have been observed to contain rolled pebbles of the very
coal through which the stream has cut its way.

The structural facts are such as to leave no alternative but to adopt the
view of the origin of such coal as I have described, which has just been
stated; but, happily, the process is not without analogy at the present
day. I possess a specimen of what is called "white coal" from Australia.
It is an inflammable material, burning with a bright flame and having
much the consistence and appearance of oat-cake, which, I am informed
covers a considerable area. It consists, almost entirely, of a compacted
mass of spores and spore-cases. But the fine particles of blown sand
which are scattered through it, show that it must have accumulated,
subaerially, upon the surface of a soil covered by a forest of
cryptogamous plants, probably tree-ferns.

As regards this important point of the subaerial region of coal, I am
glad to find myself in entire accordance with Principal Dawson, who bases
his conclusions upon other, but no less forcible, considerations. In a
passage, which is the continuation of that already cited, he writes:--

"(3) The microscopical structure and chemical composition of the beds of
cannel coal and earthy bitumen, and of the more highly bituminous and
carbonaceous shale, show them to have been of the nature of the fine
vegetable mud which accumulates in the ponds and shallow lakes of modern
swamps. When such tine vegetable sediment is mixed, as is often the case,
with clay, it becomes similar to the bituminous limestone and calcareo-
bituminous shales of the coal-measures. (4) A few of the under-clays,
which support beds of coal, are of the nature of the vegetable mud above
referred to; but the greater part are argillo-arenaceous in composition,
with little vegetable matter, and bleached by the drainage from them of
water containing the products of vegetable decay. They are, in short,
loamy or clay soils, and must have been sufficiently above water to admit
of drainage. The absence of sulphurets, and the occurrence of carbonate
of iron in connection with them, prove that, when they existed as soils,
rain-water, and not sea-water, percolated them. (5) The coal and the
fossil forests present many evidences of subaerial conditions. Most of
the erect and prostrate trees had become hollow shells of bark before
they were finally embedded, and their wood had broken into cubical pieces
of mineral charcoal. Land-snails and galley-worms (_Xylobius_) crept into
them, and they became dens, or traps, for reptiles. Large quantities of
mineral charcoal occur on the surface of all the large beds of coal. None
of these appearances could have been produced by subaqueous action. (6)
Though the roots of the _Sigillaria_ bear more resemblance to the
rhizomes of certain aquatic plants; yet, structurally, they are
absolutely identical with the roots of Cycads, which the stems also
resemble. Further, the _Sigillarioe_ grew on the same soils which
supported Conifers, _Lepidodendra_, _Cordaites_, and Ferns-plants which
could not have grown in water. Again, with the exception perhaps of some
_Pinnularioe_, and _Asterophyllites_, there is a remarkable absence from
the coal measures of any form of properly aquatic vegetation. (7) The
occurrence of marine, or brackish-water animals, in the roofs of coal-
beds, or even in the coal itself, affords no evidence of subaqueous
accumulation, since the same thing occurs in the case of modern submarine
forests. For these and other reasons, some of which are more fully stated
in the papers already referred to, while I admit that the areas of coal
accumulation were frequently submerged, I must maintain that the true
coal is a subaerial accumulation by vegetable growth on soils, wet and
swampy it is true, but not submerged."

I am almost disposed to doubt whether it is necessary to make the
concession of "wet and swampy"; otherwise, there is nothing that I know
of to be said against this excellent conspectus of the reasons for
believing in the subaerial origin of coal.

But the coal accumulated upon the area covered by one of the great
forests of the carboniferous epoch would in course of time, have been
wasted away by the small, but constant, wear and tear of rain and streams
had the land which supported it remained at the same level, or been
gradually raised to a greater elevation. And, no doubt, as much coal as
now exists has been destroyed, after its formation, in this way. What are
now known as coal districts owe their importance to the fact that they
were areas of slow depression, during a greater or less portion of the
carboniferous epoch; and that, in virtue of this circumstance, Mother
Earth was enabled to cover up her vegetable treasures, and preserve them
from destruction.

Wherever a coal-field now exists, there must formerly have been free
access for a great river, or for a shallow sea, bearing sediment in the
shape of sand and mud. When the coal-forest area became slowly depressed,
the waters must have spread over it, and have deposited their burden upon
the surface of the bed of coal, in the form of layers, which are now
converted into shale, or sandstone. Then followed a period of rest, in
which the superincumbent shallow waters became completely filled up, and
finally replaced, by fine mud, which settled down into a new under-clay,
and furnished the soil for a fresh forest growth. This flourished, and
heaped up its spores and wood into coal, until the stage of slow
depression recommenced. And, in some localities, as I have mentioned, the
process was repeated until the first of the alternating beds had sunk to
near three miles below its original level at the surface of the earth.

In reflecting on the statement, thus briefly made, of the main facts
connected with the origin of the coal formed during the carboniferous
epoch, two or three considerations suggest themselves.

In the first place, the great phantom of geological time rises before the
student of this, as of all other, fragments of the history of our earth--
springing irrepressibly out of the facts, like the Djin from the jar
which the fishermen so incautiously opened; and like the Djin again,
being vaporous, shifting, and indefinable, but unmistakably gigantic.
However modest the bases of one's calculation may be, the minimum of time
assignable to the coal period remains something stupendous.

Principal Dawson is the last person likely to be guilty of exaggeration
in this matter, and it will be well to consider what he has to say about
it:--

"The rate of accumulation of coal was very slow. The climate of the
period, in the northern temperate zone, was of such a character that the
true conifers show rings of growth, not larger, nor much less distinct,
than those of many of their modern congeners. The _Sigillarioe_ and
_Calamites_ were not, as often supposed, composed wholly, or even
principally, of lax and soft tissues, or necessarily short-lived. The
former had, it is true, a very thick inner bark; but their dense woody
axis, their thick and nearly imperishable outer bark, and their scanty
and rigid foliage, would indicate no very rapid growth or decay. In the
case of the _Sigillarioe_, the variations in the leaf-scars in different
parts of the trunk, the intercalation of new ridges at the surface
representing that of new woody wedges in the axis, the transverse marks
left by the stages of upward growth, all indicate that several years must
have been required for the growth of stems of moderate size. The enormous
roots of these trees, and the condition of the coal-swamps, must have
exempted them from the danger of being overthrown by violence. They
probably fell in successive generations from natural decay; and making
every allowance for other materials, we may safely assert that every foot
of thickness of pure bituminous coal implies the quiet growth and fall of
at least fifty generations of _Sigillarioe_, and therefore an undisturbed
condition of forest growth enduring through many centuries. Further,
there is evidence that an immense amount of loose parenchymatous tissue,
and even of wood, perished by decay, and we do not know to what extent
even the most durable tissues may have disappeared in this way; so that,
in many coal-seams, we may have only a very small part of the vegetable
matter produced."

Undoubtedly the force of these reflections is not diminished when the
bituminous coal, as in Britain, consists of accumulated spores and spore-
cases, rather than of stems. But, suppose we adopt Principal Dawson's
assumption, that one foot of coal represents fifty generations of coal
plants; and, further, make the moderate supposition that each generation
of coal plants took ten years to come to maturity--then, each foot-
thickness of coal represents five hundred years. The superimposed beds of
coal in one coal-field may amount to a thickness of fifty or sixty feet,
and therefore the coal alone, in that field, represents 500 x 50 = 25,000
years. But the actual coal is but an insignificant portion of the total
deposit, which, as has been seen, may amount to between two and three
miles of vertical thickness. Suppose it be 12,000 feet--which is 240
times the thickness of the actual coal--is there any reason why we should
believe it may not have taken 240 times as long to form? I know of none.
But, in this case, the time which the coal-field represents would be
25,000 x 240 = 6,000,000 years. As affording a definite chronology, of
course such calculations as these are of no value; but they have much use
in fixing one's attention upon a possible minimum. A man may be puzzled
if he is asked how long Rome took a-building; but he is proverbially safe
if he affirms it not to have been built in a day; and our geological
calculations are all, at present, pretty much on that footing.

A second consideration which the study of the coal brings prominently
before the mind of any one who is familiar with palaeontology is, that the
coal Flora, viewed in relation to the enormous period of time which it
lasted, and to the still vaster period which has elapsed since it
flourished, underwent little change while it endured, and in its peculiar
characters, differs strangely little from that which at present exist.

The same species of plants are to be met with throughout the whole
thickness of a coal-field, and the youngest are not sensibly different
from the oldest. But more than this. Notwithstanding that the
carboniferous period is separated from us by more than the whole time
represented by the secondary and tertiary formations, the great types of
vegetation were as distinct then as now. The structure of the modern
club-moss furnishes a complete explanation of the fossil remains of the
_Lepidodendra_, and the fronds of some of the ancient ferns are hard to
distinguish from existing ones. At the same time, it must be remembered,
that there is nowhere in the world, at present, any _forest_ which bears
more than a rough analogy with a coal-forest. The types may remain, but
the details of their form, their relative proportions, their associates,
are all altered. And the tree-fern forest of Tasmania, or New Zealand,
gives one only a faint and remote image of the vegetation of the ancient
world.

Once more, an invariably-recurring lesson of geological history, at
whatever point its study is taken up: the lesson of the almost infinite
slowness of the modification of living forms. The lines of the pedigrees
of living things break off almost before they begin to converge.

Finally, yet another curious consideration. Let us suppose that one of
the stupid, salamander-like Labyrinthodonts, which pottered, with much
belly and little leg, like Falstaff in his old age, among the coal-
forests, could have had thinking power enough in his small brain to
reflect upon the showers of spores which kept on falling through years
and centuries, while perhaps not one in ten million fulfilled its
apparent purpose, and reproduced the organism which gave it birth: surely
he might have been excused for moralizing upon the thoughtless and wanton
extravagance which Nature displayed in her operations.

But we have the advantage over our shovel-headed predecessor--or possibly
ancestor--and can perceive that a certain vein of thrift runs through
this apparent prodigality. Nature is never in a hurry, and seems to have
had always before her eyes the adage, "Keep a thing long enough, and you
will find a use for it." She has kept her beds of coal many millions of
years without being able to find much use for them; she has sent them
down beneath the sea, and the sea-beasts could make nothing of them; she
has raised them up into dry land, and laid the black veins bare, and
still, for ages and ages, there was no living thing on the face of the
earth that could see any sort of value in them; and it was only the other
day, so to speak, that she turned a new creature out of her workshop, who
by degrees acquired sufficient wits to make a fire, and then to discover
that the black rock would burn.

I suppose that nineteen hundred years ago, when Julius Caesar was good
enough to deal with Britain as we have dealt with New Zealand, the
primaeval Briton, blue with cold and woad, may have known that the strange
black stone, of which he found lumps here and there in his wanderings,
would burn, and so help to warm his body and cook his food. Saxon, Dane,
and Norman swarmed into the land. The English people grew into a powerful
nation, and Nature still waited for a full return of the capital she had
invested in the ancient club-mosses. The eighteenth century arrived, and
with it James Watt. The brain of that man was the spore out of which was
developed the modern steam-engine, and all the prodigious trees and
branches of modern industry which have grown out of this. But coal is as
much an essential condition of this growth and development as carbonic
acid is for that of a club-moss. Wanting coal, we could not have smelted
the iron needed to make our engines, nor have worked our engines when we
had got them. But take away the engines, and the great towns of Yorkshire
and Lancashire vanish like a dream. Manufactures give place to
agriculture and pasture, and not ten men can live where now ten thousand
are amply supported.

Thus, all this abundant wealth of money and of vivid life is Nature's
interest upon her investment in club-mosses, and the like, so long ago.
But what becomes of the coal which is burnt in yielding this interest?
Heat comes out of it, light comes out of it; and if we could gather
together all that goes up the chimney, and all that remains in the grate
of a thoroughly-burnt coal-fire, we should find ourselves in possession
of a quantity of carbonic acid, water, ammonia, and mineral matters,
exactly equal in weight to the coal. But these are the very matters with
which Nature supplied the club-mosses which made the coal She is paid
back principal and interest at the same time; and she straightway invests
the carbonic acid, the water, and the ammonia in new forms of life,
feeding with them the plants that now live. Thrifty Nature! Surely no
prodigal, but most notable of housekeepers!



VI


ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS

[1876]

In the whole history of science there is nothing more remarkable than the
rapidity of the growth of biological knowledge within the last half-
century, and the extent of the modification which has thereby been
effected in some of the fundamental conceptions of the naturalist.

In the second edition of the "Regne Animal," published in 1828, Cuvier
devotes a special section to the "Division of Organised Beings into
Animals and Vegetables," in which the question is treated with that
comprehensiveness of knowledge and clear critical judgment which
characterise his writings, and justify us in regarding them as
representative expressions of the most extensive, if not the profoundest,
knowledge of his time. He tells us that living beings have been
subdivided from the earliest times into _animated beings_, which possess
sense and motion, and _inanimated beings_, which are devoid of these
functions and simply vegetate.

Although the roots of plants direct themselves towards moisture, and
their leaves towards air and light,--although the parts of some plants
exhibit oscillating movements without any perceptible cause, and the
leaves of others retract when touched,--yet none of these movements
justify the ascription to plants of perception or of will. From the
mobility of animals, Cuvier, with his characteristic partiality for
teleological reasoning, deduces the necessity of the existence in them of
an alimentary cavity, or reservoir of food, whence their nutrition may be
drawn by the vessels, which are a sort of internal roots; and, in the
presence of this alimentary cavity, he naturally sees the primary and the
most important distinction between animals and plants.

Following out his teleological argument, Cuvier remarks that the
organisation of this cavity and its appurtenances must needs vary
according to the nature of the aliment, and the operations which it has
to undergo, before it can be converted into substances fitted for
absorption; while the atmosphere and the earth supply plants with juices
ready prepared, and which can be absorbed immediately. As the animal body
required to be independent of heat and of the atmosphere, there were no
means by which the motion of its fluids could be produced by internal
causes. Hence arose the second great distinctive character of animals, or
the circulatory system, which is less important than the digestive, since
it was unnecessary, and therefore is absent, in the more simple animals.

Animals further needed muscles for locomotion and nerves for sensibility.
Hence, says Cuvier, it was necessary that the chemical composition of the
animal body should be more complicated than that of the plant; and it is
so, inasmuch as an additional substance, nitrogen, enters into it as an
essential element; while, in plants, nitrogen is only accidentally joined
with he three other fundamental constituents of organic beings--carbon,
hydrogen, and oxygen. Indeed, he afterwards affirms that nitrogen is
peculiar to animals; and herein he places the third distinction between
the animal and the plant. The soil and the atmosphere supply plants with
water, composed of hydrogen and oxygen; air, consisting of nitrogen and
oxygen; and carbonic acid, containing carbon and oxygen. They retain the
hydrogen and the carbon, exhale the superfluous oxygen, and absorb little
or no nitrogen. The essential character of vegetable life is the
exhalation of oxygen, which is effected through the agency of light.
Animals, on the contrary, derive their nourishment either directly or
indirectly from plants. They get rid of the superfluous hydrogen and
carbon, and accumulate nitrogen. The relations of plants and animals to
the atmosphere are therefore inverse. The plant withdraws water and
carbonic acid from the atmosphere, the animal contributes both to it.
Respiration--that is, the absorption of oxygen and the exhalation of
carbonic acid--is the specially animal function of animals, and
constitutes their fourth distinctive character.

Thus wrote Cuvier in 1828. But, in the fourth and fifth decades of this
century, the greatest and most rapid revolution which biological science
has ever undergone was effected by the application of the modern
microscope to the investigation of organic structure; by the introduction
of exact and easily manageable methods of conducting the chemical
analysis of organic compounds; and finally, by the employment of
instruments of precision for the measurement of the physical forces which
are at work in the living economy.

That the semi-fluid contents (which we now term protoplasm) of the cells
of certain plants, such as the _Charoe_ are in constant and regular
motion, was made out by Bonaventura Corti a century ago; but the fact,
important as it was, fell into oblivion, and had to be rediscovered by
Treviranus in 1807. Robert Brown noted the more complex motions of the
protoplasm in the cells of _Tradescantia_ in 1831; and now such movements
of the living substance of plants are well known to be some of the most
widely-prevalent phenomena of vegetable life.

Agardh, and other of the botanists of Cuvier's generation, who occupied
themselves with the lower plants, had observed that, under particular
circumstances, the contents of the cells of certain water-weeds were set
free, and moved about with considerable velocity, and with all the
appearances of spontaneity, as locomotive bodies, which, from their
similarity to animals of simple organisation, were called "zoospores."
Even as late as 1845, however, a botanist of Schleiden's eminence dealt
very sceptically with these statements; and his scepticism was the more
justified, since Ehrenberg, in his elaborate and comprehensive work on
the _Infusoria_, had declared the greater number of what are now
recognised as locomotive plants to be animals.

At the present day, innumerable plants and free plant cells are known to
pass the whole or part of their lives in an actively locomotive
condition, in no wise distinguishable from that of one of the simpler
animals; and, while in this condition, their movements are, to all
appearance, as spontaneous--as much the product of volition--as those of
such animals.

Hence the teleological argument for Cuvier's first diagnostic character--
the presence in animals of an alimentary cavity, or internal pocket, in
which they can carry about their nutriment--has broken down, so far, at
least, as his mode of stating it goes. And, with the advance of
microscopic anatomy, the universality of the fact itself among animals
has ceased to be predicable. Many animals of even complex structure,
which live parasitically within others, are wholly devoid of an
alimentary cavity. Their food is provided for them, not only ready
cooked, but ready digested, and the alimentary canal, become superfluous,
has disappeared. Again, the males of most Rotifers have no digestive
apparatus; as a German naturalist has remarked, they devote themselves
entirely to the "Minnedienst," and are to be reckoned among the few
realisations of the Byronic ideal of a lover. Finally, amidst the lowest
forms of animal life, the speck of gelatinous protoplasm, which
constitutes the whole body, has no permanent digestive cavity or mouth,
but takes in its food anywhere; and digests, so to speak, all over its
body. But although Cuvier's leading diagnosis of the animal from the
plant will not stand a strict test, it remains one of the most constant
of the distinctive characters of animals. And, if we substitute for the
possession of an alimentary cavity, the power of taking solid nutriment
into the body and there digesting it, the definition so changed will
cover all animals except certain parasites, and the few and exceptional
cases of non-parasitic animals which do not feed at all. On the other
hand, the definition thus amended will exclude all ordinary vegetable
organisms.

Cuvier himself practically gives up his second distinctive mark when he
admits that it is wanting in the simpler animals.

The third distinction is based on a completely erroneous conception of
the chemical differences and resemblances between the constituents of
animal and vegetable organisms, for which Cuvier is not responsible, as
it was current among contemporary chemists. It is now established that
nitrogen is as essential a constituent of vegetable as of animal living
matter; and that the latter is, chemically speaking, just as complicated
as the former. Starchy substances, cellulose and sugar, once supposed to
be exclusively confined to plants, are now known to be regular and normal
products of animals. Amylaceous and saccharine substances are largely
manufactured, even by the highest animals; cellulose is widespread as a
constituent of the skeletons of the lower animals; and it is probable
that amyloid substances are universally present in the animal organism,
though not in the precise form of starch.

Moreover, although it remains true that there is an inverse relation
between the green plant in sunshine and the animal, in so far as, under
these circumstances, the green plant decomposes carbonic acid and exhales
oxygen, while the animal absorbs oxygen and exhales carbonic acid; yet,
the exact researches of the modern chemical investigators of the
physiological processes of plants have clearly demonstrated the fallacy
of attempting to draw any general distinction between animals and
vegetables on this ground. In fact, the difference vanishes with the
sunshine, even in the case of the green plant; which, in the dark,
absorbs oxygen and gives out carbonic acid like any animal.[1] On the
other hand, those plants, such as the fungi, which contain no chlorophyll
and are not green, are always, so far as respiration is concerned, in the
exact position of animals. They absorb oxygen and give out carbonic acid.

[Footnote 1: There is every reason to believe that living plants, like
living animals, always respire, and, in respiring, absorb oxygen and give
off carbonic acid; but, that in green plants exposed to daylight or to
the electric light, the quantity of oxygen evolved in consequence of the
decomposition of carbonic acid by a special apparatus which green plants
possess exceeds that absorbed in the concurrent respiratory process.]

Thus, by the progress of knowledge, Cuvier's fourth distinction between
the animal and the plant has been as completely invalidated as the third
and second; and even the first can be retained only in a modified form
and subject to exceptions.

But has the advance of biology simply tended to break down old
distinctions, without establishing new ones?

With a qualification, to be considered presently, the answer to this
question is undoubtedly in the affirmative. The famous researches of
Schwann and Schleiden in 1837 and the following years, founded the modern
science of histology, or that branch of anatomy which deals with the
ultimate visible structure of organisms, as revealed by the microscope;
and, from that day to this, the rapid improvement of methods of
investigation, and the energy of a host of accurate observers, have given
greater and greater breadth and firmness to Schwann's great
generalisation, that a fundamental unity of structure obtains in animals
and plants; and that, however diverse may be the fabrics, or _tissues_,
of which their bodies are composed, all these varied structures result
from the metamorphosis of morphological units (termed _cells_, in a more
general sense than that in which the word "cells" was at first employed),
which are not only similar in animals and in plants respectively, but
present a close resemblance, when those of animals and those of plants
are compared together.

The contractility which is the fundamental condition of locomotion, has
not only been discovered to exist far more widely among plants than was
formerly imagined; but, in plants, the act of contraction has been found
to be accompanied, as Dr. Burdon Sanderson's interesting investigations
have shown, by a disturbance of the electrical state of the contractile
substance, comparable to that which was found by Du Bois Reymond to be a
concomitant of the activity of ordinary muscle in animals.

Again, I know of no test by which the reaction of the leaves of the
Sundew and of other plants to stimuli, so fully and carefully studied by
Mr. Darwin, can be distinguished from those acts of contraction following
upon stimuli, which are called "reflex" in animals.

On each lobe of the bilobed leaf of Venus's fly-trap (_Dionoea
muscipula_) are three delicate filaments which stand out at right angle
from the surface of the leaf. Touch one of them with the end of a fine
human hair and the lobes of the leaf instantly close together[2] in
virtue of an act of contraction of part of their substance, just as the
body of a snail contracts into its shell when one of its "horns" is
irritated.

[Footnote 2: Darwin, _Insectivorous Plants_, p. 289.]

The reflex action of the snail is the result of the presence of a nervous
system in the animal. A molecular change takes place in the nerve of the
tentacle, is propagated to the muscles by which the body is retracted,
and causing them to contract, the act of retraction is brought about. Of
course the similarity of the acts does not necessarily involve the
conclusion that the mechanism by which they are effected is the same; but
it suggests a suspicion of their identity which needs careful testing.

The results of recent inquiries into the structure of the nervous system
of animals converge towards the conclusion that the nerve fibres, which
we have hitherto regarded as ultimate elements of nervous tissue, are not
such, but are simply the visible aggregations of vastly more attenuated
filaments, the diameter of which dwindles down to the limits of our
present microscopic vision, greatly as these have been extended by modern
improvements of the microscope; and that a nerve is, in its essence,
nothing but a linear tract of specially modified protoplasm between two
points of an organism--one of which is able to affect the other by means
of the communication so established. Hence, it is conceivable that even
the simplest living being may possess a nervous system. And the question
whether plants are provided with a nervous system or not, thus acquires a
new aspect, and presents the histologist and physiologist with a problem
of extreme difficulty, which must be attacked from a new point of view
and by the aid of methods which have yet to be invented.

Thus it must be admitted that plants may be contractile and locomotive;
that, while locomotive, their movements may have as much appearance of
spontaneity as those of the lowest animals; and that many exhibit
actions, comparable to those which are brought about by the agency of a
nervous system in animals. And it must be allowed to be possible that
further research may reveal the existence of something comparable to a
nervous system in plants. So that I know not where we can hope to find
any absolute distinction between animals and plants, unless we return to
their mode of nutrition, and inquire whether certain differences of a
more occult character than those imagined to exist by Cuvier, and which
certainly hold good for the vast majority of animals and plants, are of
universal application.

A bean may be supplied with water in which salts of ammonia and certain
other mineral salts are dissolved in due proportion; with atmospheric air
containing its ordinary minute dose of carbonic acid; and with nothing
else but sunlight and heat. Under these circumstances, unnatural as they
are, with proper management, the bean will thrust forth its radicle and
its plumule; the former will grow down into roots, the latter grow up
into the stem and leaves of a vigorous bean-plant; and this plant will,
in due time, flower and produce its crop of beans, just as if it were
grown in the garden or in the field.

The weight of the nitrogenous protein compounds, of the oily, starchy,
saccharine and woody substances contained in the full-grown plant and its
seeds, will be vastly greater than the weight of the same substances
contained in the bean from which it sprang. But nothing has been supplied
to the bean save water, carbonic acid, ammonia, potash, lime, iron, and
the like, in combination with phosphoric, sulphuric, and other acids.
Neither protein, nor fat, nor starch, nor sugar, nor any substance in the
slightest degree resembling them, has formed part of the food of the
bean. But the weights of the carbon, hydrogen, oxygen, nitrogen,
phosphorus, sulphur, and other elementary bodies contained in the bean-
plant, and in the seeds which it produces, are exactly equivalent to the
weights of the same elements which have disappeared from the materials
supplied to the bean during its growth. Whence it follows that the bean
has taken in only the raw materials of its fabric, and has manufactured
them into bean-stuffs.

The bean has been able to perform this great chemical feat by the help of
its green colouring matter, or chlorophyll; for it is only the green
parts of the plant which, under the influence of sunlight, have the
marvellous power of decomposing carbonic acid, setting free the oxygen
and laying hold of the carbon which it contains. In fact, the bean
obtains two of the absolutely indispensable elements of its substance
from two distinct sources; the watery solution, in which its roots are
plunged, contains nitrogen but no carbon; the air, to which the leaves
are exposed, contains carbon, but its nitrogen is in the state of a free
gas, in which condition the bean can make no use of it;[3] and the
chlorophyll[4] is the apparatus by which the carbon is extracted from the
atmospheric carbonic acid--the leaves being the chief laboratories in
which this operation is effected.

[Footnote 3: I purposely assume that the air with which the bean is
supplied in the case stated contains no ammoniacal salts.]

[Footnote 4: The recent researches of Pringsheim have raised a host of
questions as to the exact share taken by chlorophyll in the chemical
operations which are effected by the green parts of plants. It may be
that the chlorophyll is only a constant concomitant of the actual
deoxidising apparatus.]

The great majority of conspicuous plants are, as everybody knows, green;
and this arises from the abundance of their chlorophyll. The few which
contain no chlorophyll and are colourless, are unable to extract the
carbon which they require from atmospheric carbonic acid, and lead a
parasitic existence upon other plants; but it by no means follows, often
as the statement has been repeated, that the manufacturing power of
plants depends on their chlorophyll, and its interaction with the rays of
the sun. On the contrary, it is easily demonstrated, as Pasteur first
proved, that the lowest fungi, devoid of chlorophyll, or of any
substitute for it, as they are, nevertheless possess the characteristic
manufacturing powers of plants in a very high degree. Only it is
necessary that they should be supplied with a different kind of raw
material; as they cannot extract carbon from carbonic acid, they must be
furnished with something else that contains carbon. Tartaric acid is such
a substance; and if a single spore of the commonest and most troublesome
of moulds--_Penicillium_--be sown in a saucerful of water, in which
tartrate of ammonia, with a small percentage of phosphates and sulphates
is contained, and kept warm, whether in the dark or exposed to light, it
will, in a short time, give rise to a thick crust of mould, which
contains many million times the weight of the original spore, in protein
compounds and cellulose. Thus we have a very wide basis of fact for the
generalisation that plants are essentially characterised by their
manufacturing capacity--by their power of working up mere mineral matters
into complex organic compounds.

Contrariwise, there is a no less wide foundation for the generalisation
that animals, as Cuvier puts it, depend directly or indirectly upon
plants for the materials of their bodies; that is, either they are
herbivorous, or they eat other animals which are herbivorous.

But for what constituents of their bodies are animals thus dependent upon
plants? Certainly not for their horny matter; nor for chondrin, the
proximate chemical element of cartilage; nor for gelatine; nor for
syntonin, the constituent of muscle; nor for their nervous or biliary
substances; nor for their amyloid matters; nor, necessarily, for their
fats.

It can be experimentally demonstrated that animals can make these for
themselves. But that which they cannot make, but must, in all known
cases, obtain directly or indirectly from plants, is the peculiar
nitrogenous matter, protein. Thus the plant is the ideal _proletaire_ of
the living world, the worker who produces; the animal, the ideal
aristocrat, who mostly occupies himself in consuming, after the manner of
that noble representative of the line of Zaehdarm, whose epitaph is
written in "Sartor Resartus."

Here is our last hope of finding a sharp line of demarcation between
plants and animals; for, as I have already hinted, there is a border
territory between the two kingdoms, a sort of no-man's-land, the
inhabitants of which certainly cannot be discriminated and brought to
their proper allegiance in any other way.

Some months ago, Professor Tyndall asked me to examine a drop of infusion
of hay, placed under an excellent and powerful microscope, and to tell
him what I thought some organisms visible in it were. I looked and
observed, in the first place, multitudes of _Bacteria_ moving about with
their ordinary intermittent spasmodic wriggles. As to the vegetable
nature of these there is now no doubt. Not only does the close
resemblance of the _Bacteria_ to unquestionable plants, such as the
_Oscillatorioe_ and the lower forms of _Fungi_, justify this conclusion,
but the manufacturing test settles the question at once. It is only
needful to add a minute drop of fluid containing _Bacteria_, to water in
which tartrate, phosphate, and sulphate of ammonia are dissolved; and, in
a very short space of time, the clear fluid becomes milky by reason of
their prodigious multiplication, which, of course, implies the
manufacture of living Bacterium-stuff out of these merely saline matters.

But other active organisms, very much larger than the _Bacteria_,
attaining in fact the comparatively gigantic dimensions of 1/3000 of an
inch or more, incessantly crossed the field of view. Each of these had a
body shaped like a pear, the small end being slightly incurved and
produced into a long curved filament, or _cilium_, of extreme tenuity.
Behind this, from the concave side of the incurvation, proceeded another
long cilium, so delicate as to be discernible only by the use of the
highest powers and careful management of the light. In the centre of the
pear-shaped body a clear round space could occasionally be discerned, but
not always; and careful watching showed that this clear vacuity appeared
gradually, and then shut up and disappeared suddenly, at regular
intervals. Such a structure is of common occurrence among the lowest
plants and animals, and is known as a _contractile vacuole_.

The little creature thus described sometimes propelled itself with great
activity, with a curious rolling motion, by the lashing of the front
cilium, while the second cilium trailed behind; sometimes it anchored
itself by the hinder cilium and was spun round by the working of the
other, its motions resembling those of an anchor buoy in a heavy sea.
Sometimes, when two were in full career towards one another, each would
appear dexterously to get out of the other's way; sometimes a crowd would
assemble and jostle one another, with as much semblance of individual
effort as a spectator on the Grands Mulets might observe with a telescope
among the specks representing men in the valley of Chamounix.

The spectacle, though always surprising, was not new to me. So my reply
to the question put to me was, that these organisms were what biologists
call _Monads_, and though they might be animals, it was also possible
that they might, like the _Bacteria_, be plants. My friend received my
verdict with an expression which showed a sad want of respect for
authority. He would as soon believe that a sheep was a plant. Naturally
piqued by this want of faith, I have thought a good deal over the matter;
and, as I still rest in the lame conclusion I originally expressed, and
must even now confess that I cannot certainly say whether this creature
is an animal or a plant, I think it may be well to state the grounds of
my hesitation at length. But, in the first place, in order that I may
conveniently distinguish this "Monad" from the multitude of other things
which go by the same designation, I must give it a name of its own. I
think (though, for reasons which need not be stated at present, I am not
quite sure) that it is identical with the species _Monas lens_ as defined
by the eminent French microscopist Dujardin, though his magnifying power
was probably insufficient to enable him to see that it is curiously like
a much larger form of monad which he has named _Heteromita_. I shall,
therefore, call it not _Monas_, but _Heteromita lens_.

I have been unable to devote to my _Heteromita_ the prolonged study
needful to work out its whole history, which would involve weeks, or it
may be months, of unremitting attention. But I the less regret this
circumstance, as some remarkable observations recently published by
Messrs. Dallinger and Drysdale[5] on certain Monads, relate, in part, to
a form so similar to my _Heteromita lens_, that the history of the one
may be used to illustrate that of the other. These most patient and
painstaking observers, who employed the highest attainable powers of the
microscope and, relieving one another, kept watch day and night over the
same individual monads, have been enabled to trace out the whole history
of their _Heteromita_; which they found in infusions of the heads of
fishes of the Cod tribe.

[Footnote 5: "Researches in the Life-history of a Cercomonad: a Lesson in
Biogenesis"; and "Further Researches in the Life-history of the Monads,"
--_Monthly Microscopical Journal_, 1873.]

Of the four monads described and figured by these investigators, one, as
I have said, very closely resembles _Heteromita lens_ in every
particular, except that it has a separately distinguishable central
particle or "nucleus," which is not certainly to be made out in
_Heteromita lens_; and that nothing is said by Messrs. Dallinger and
Drysdale of the existence of a contractile vacuole in this monad, though
they describe it in another.

Their _Heteromita_, however, multiplied rapidly by fission. Sometimes a
transverse constriction appeared; the hinder half developed a new cilium,
and the hinder cilium gradually split from its base to its free end,
until it was divided into two; a process which, considering the fact that
this fine filament cannot be much more than 1/100000 of an inch in
diameter, is wonderful enough. The constriction of the body extended
inwards until the two portions were united by a narrow isthmus; finally,
they separated and each swam away by itself, a complete _Heteromita_,
provided with its two cilia. Sometimes the constriction took a
longitudinal direction, with the same ultimate result. In each case the
process occupied not more than six or seven minutes. At this rate, a
single _Heteromita_ would give rise to a thousand like itself in the
course of an hour, to about a million in two hours, and to a number
greater than the generally assumed number of human beings now living in
the world in three hours; or, if we give each _Heteromita_ an hour's
enjoyment of individual existence, the same result will be obtained in
about a day. The apparent suddenness of the appearance of multitudes of
such organisms as these in any nutritive fluid to which one obtains
access is thus easily explained.

During these processes of multiplication by fission, the _Heteromita_
remains active; but sometimes another mode of fission occurs. The body
becomes rounded and quiescent, or nearly so; and, while in this resting
state, divides into two portions, each of which is rapidly converted into
an active _Heteromita_.

A still more remarkable phenomenon is that kind of multiplication which
is preceded by the union of two monads, by a process which is termed
_conjugation_. Two active _Heteromitoe_ become applied to one another,
and then slowly and gradually coalesce into one body. The two nuclei run
into one; and the mass resulting from the conjugation of the two
_Heteromitoe_, thus fused together, has a triangular form. The two pairs
of cilia are to be seen, for some time, at two of the angles, which
answer to the small ends of the conjoined monads; but they ultimately
vanish, and the twin organism, in which all visible traces of
organisation have disappeared, falls into a state of rest. Sudden wave-
like movements of its substance next occur; and, in a short time, the
apices of the triangular mass burst, and give exit to a dense yellowish,
glairy fluid, filled with minute granules. This process, which, it will
be observed, involves the actual confluence and mixture of the substance
of two distinct organisms, is effected in the space of about two hours.

The authors whom I quote say that they "cannot express" the excessive
minuteness of the granules in question, and they estimate their diameter
at less than 1/200000 of an inch. Under the highest powers of the
microscope, at present applicable, such specks are hardly discernible.
Nevertheless, particles of this size are massive when compared to
physical molecules; whence there is no reason to doubt that each, small
as it is, may have a molecular structure sufficiently complex to give
rise to the phenomena of life. And, as a matter of fact, by patient
watching of the place at which these infinitesimal living particles were
discharged, our observers assured themselves of their growth and
development into new monads. In about four hours from their being set
free, they had attained a sixth of the length of the parent, with the
characteristic cilia, though at first they were quite motionless; and, in
four hours more, they had attained the dimensions and exhibited all the
activity of the adult. These inconceivably minute particles are therefore
the germs of the _Heteromita_; and from the dimensions of these germs it
is easily shown that the body formed by conjugation may, at a low
estimate, have given exit to thirty thousand of them; a result of a
matrimonial process whereby the contracting parties, without a metaphor,
"become one flesh," enough to make a Malthusian despair of the future of
the Universe.

I am not aware that the investigators from whom I have borrowed this
history have endeavoured to ascertain whether their monads take solid
nutriment or not; so that though they help us very much to fill up the
blanks in the history of my _Heteromita_, their observations throw no
light on the problem we are trying to solve--Is it an animal or is it a
plant?

Undoubtedly it is possible to bring forward very strong arguments in
favour of regarding _Heteromita_ as a plant.

For example, there is a Fungus, an obscure and almost microscopic mould,
termed _Peronospora infestans_. Like many other Fungi, the _Peronosporoe_
are parasitic upon other plants; and this particular _Peronospora_
happens to have attained much notoriety and political importance, in a
way not without a parallel in the career of notorious politicians,
namely, by reason of the frightful mischief it has done to mankind. For
it is this _Fungus_ which is the cause of the potato disease; and,
therefore, _Peronospora infestans_ (doubtless of exclusively Saxon
origin, though not accurately known to be so) brought about the Irish
famine. The plants afflicted with the malady are found to be infested by
a mould, consisting of fine tubular filaments, termed _hyphoe_, which
burrow through the substance of the potato plant, and appropriate to
themselves the substance of their host; while, at the same time, directly
or indirectly, they set up chemical changes by which even its woody
framework becomes blackened, sodden, and withered.

In structure, however, the _Peronospora_ is as much a mould as the common
_Penicillium_; and just as the _Penicillium_ multiplies by the breaking
up of its hyphoe into separate rounded bodies, the spores; so, in the
_Peronospora_, certain of the hyphoe grow out into the air through the
interstices of the superficial cells of the potato plant, and develop
spores. Each of these hyphoe usually gives off several branches. The ends
of the branches dilate and become closed sacs, which eventually drop off
as spores. The spores falling on some part of the same potato plant, or
carried by the wind to another, may at once germinate, throwing out
tubular prolongations which become hyphoe, and burrow into the substance
of the plant attacked. But, more commonly, the contents of the spore
divide into six or eight separate portions. The coat of the spore gives
way, and each portion then emerges as an independent organism, which has
the shape of a bean, rather narrower at one end than the other, convex on
one side, and depressed or concave on the opposite. From the depression,
two long and delicate cilia proceed, one shorter than the other, and
directed forwards. Close to the origin of these cilia, in the substance
of the body, is a regularly pulsating, contractile vacuole. The shorter
cilium vibrates actively, and effects the locomotion of the organism,
while the other trails behind; the whole body rolling on its axis with
its pointed end forwards.

The eminent botanist, De Bary, who was not thinking of our problem, tells
us, in describing the movements of these "Zoospores," that, as they swim
about, "Foreign bodies are carefully avoided, and the whole movement has
a deceptive likeness to the voluntary changes of place which are observed
in microscopic animals."

After swarming about in this way in the moisture on the surface of a leaf
or stem (which, film though it may be, is an ocean to such a fish) for
half an hour, more or less, the movement of the zoospore becomes slower,
and is limited to a slow turning upon its axis, without change of place.
It then becomes quite quiet, the cilia disappear, it assumes a spherical
form, and surrounds itself with a distinct, though delicate, membranous
coat. A protuberance then grows out from one side of the sphere, and
rapidly increasing in length, assumes the character of a hypha. The
latter penetrates into the substance of the potato plant, either by
entering a stomate, or by boring through the wall of an epidermic cell,
and ramifies, as a mycelium, in the substance of the plant, destroying
the tissues with which it comes in contact. As these processes of
multiplication take place very rapidly, millions of spores are soon set
free from a single infested plant; and, from their minuteness, they are
readily transported by the gentlest breeze. Since, again, the zoospores
set free from each spore, in virtue of their powers of locomotion,
swiftly disperse themselves over the surface, it is no wonder that the
infection, once started, soon spreads from field to field, and extends
its ravages over a whole country.

However, it does not enter into my present plan to treat of the potato
disease, instructively as its history bears upon that of other epidemics;
and I have selected the case of the _Peroganspora_ simply because it
affords an example of an organism, which, in one stage of its existence,
is truly a "Monad," indistinguishable by any important character from our
_Heteromita_, and extraordinarily like it in some respects. And yet this
"Monad" can be traced, step by step, through the series of metamorphoses
which I have described, until it assumes the features of an organism,
which is as much a plant as is an oak or an elm.

Moreover, it would be possible to pursue the analogy farther. Under
certain circumstances, a process of conjugation takes place in the
_Peronospora_. Two separate portions of its protoplasm become fused
together, surround themselves with a thick coat and give rise to a sort
of vegetable egg called an _oospore_. After a period of rest, the
contents of the oospore break up into a number of zoospores like those
already described, each of which, after a period of activity, germinates
in the ordinary way. This process obviously corresponds with the
conjugation and subsequent setting free of germs in the _Heteromita_.

But it may be said that the _Peronospora_ is, after all, a questionable
sort of plant; that it seems to be wanting in the manufacturing power,
selected as the main distinctive character of vegetable life; or, at any
rate, that there is no proof that it does not get its protein matter
ready made from the potato plant.

Let us, therefore, take a case which is not open to these objections.

There are some small plants known to botanists as members of the genus
_Colcochaete_, which, without being truly parasitic, grow upon certain
water-weeds, as lichens grow upon trees. The little plant has the form of
an elegant green star, the branching arms of which are divided into
cells. Its greenness is due to its chlorophyll, and it undoubtedly has
the manufacturing power in full degree, decomposing carbonic acid and
setting oxygen free, under the influence of sunlight. But the
protoplasmic contents of some of the cells of which the plant is made up
occasionally divide, by a method similar to that which effects the
division of the contents of the _Peronospora_ spore; and the severed
portions are then set free as active monad-like zoospores. Each is oval
and is provided at one extremity with two long active cilia. Propelled by
these, it swims about for a longer or shorter time, but at length comes
to a state of rest and gradually grows into a _Coleochaete_. Moreover, as
in the _Peronospora_, conjugation may take place and result in an
oospore; the contents of which divide and are set free as monadiform
germs.

If the whole history of the zoospores of _Peronospora_ and of
_Coleochaete_ were unknown, they would undoubtedly be classed among
"Monads" with the same right as _Heteromita_; why then may not
_Heteromita_ be a plant, even though the cycle of forms through which it
passes shows no terms quite so complex as those which occur in
_Peronospora_ and _Coleochaete_? And, in fact, there are some green
organisms, in every respect characteristically plants, such as
_Chlamydomonas_, and the common _Volvox_, or so-called "Globe
animalcule," which run through a cycle of forms of just the same simple
character as those of _Heteromita_.

The name of _Chlamydomonas_ is applied to certain microscopic green
bodies, each of which consists of a protoplasmic central substance
invested by a structureless sac. The latter contains cellulose, as in
ordinary plants; and the chlorophyll which gives the green colour enables
the _Chlamydomonas_ to decompose carbonic acid and fix carbon as they do.
Two long cilia protrude through the cell-wall, and effect the rapid
locomotion of this "monad," which, in all respects except its mobility,
is characteristically a plant. Under ordinary circumstances, the
_Chlamydomonas_ multiplies by simple fission, each splitting into two or
into four parts, which separate and become independent organisms.
Sometimes, however, the _Chlamydomonas_ divides into eight parts, each of
which is provided with four instead of two cilia. These "zoospores"
conjugate in pairs, and give rise to quiescent bodies, which multiply by
division, find eventually pass into the active state.

Thus, so far as outward form and the general character of the cycle of
modifications, through which the organism passes in the course of its
life, are concerned, the resemblance between _Chlamydomonas_ and
_Heteromita_ is of the closest description. And on the face of the matter
there is no ground for refusing to admit that _Heteromita_ may be related
to _Chlamydomonas_, as the colourless fungus is to the green alga.
_Volvox_ may be compared to a hollow sphere, the wall of which is made up
of coherent Chlamydomonads; and which progresses with a rotating motion
effected by the paddling of the multitudinous pairs of cilia which
project from its surface. Each _Volvox_-monad, moreover, possesses a red
pigment spot, like the simplest form of eye known among animals. The
methods of fissive multiplication and of conjugation observed in the
monads of this locomotive globe are essentially similar to those observed
in _Chlamydomonas_; and, though a hard battle has been fought over it,
_Volvox_ is now finally surrendered to the Botanists.

Thus there is really no reason why _Heteromita_ may not be a plant; and
this conclusion would be very satisfactory, if it were not equally easy
to show that there is really no reason why it should not be an animal.
For there are numerous organisms presenting the closest resemblance to
_Heteromita_, and, like it, grouped under the general name of "Monads,"
which, nevertheless, can be observed to take in solid nutriment, and
which, therefore, have a virtual, if not an actual, mouth and digestive
cavity, and thus come under Cuvier's definition of an animal. Numerous
forms of such animals have been described by Ehrenberg, Dujardin, H.
James Clark, and other writers on the _Infusoria_. Indeed, in another
infusion of hay in which my _Heteromita lens_ occurred, there were
innumerable such infusorial animalcules belonging to the well-known
species _Colpoda cucullus_.[6]

[Footnote 6: Excellently described by Stein, almost all of whose
statements I have verified.]

Full-sized specimens of this animalcule attain a length of between 1/300
or 1/400 of an inch, so that it may have ten times the length and a
thousand times the mass of a _Heteromita_. In shape, it is not altogether
unlike _Heteromita_. The small end, however, is not produced into one
long cilium, but the general surface of the body is covered with small
actively vibrating ciliary organs, which are only longest at the small
end. At the point which answers to that from which the two cilia arise in
_Heteromita_, there is a conical depression, the mouth; and, in young
specimens, a tapering filament, which reminds one of the posterior cilium
of _Heteromita_, projects from this region.

The body consists of a soft granular protoplasmic substance, the middle
of which is occupied by a large oval mass called the "nucleus"; while, at
its hinder end, is a "contractile vacuole," conspicuous by its regular
rhythmic appearances and disappearances. Obviously, although the
_Colpoda_ is not a monad, it differs from one only in subordinate
details. Moreover, under certain conditions, it becomes quiescent,
incloses itself in a delicate case or _cyst_, and then divides into two,
four, or more portions, which are eventually set free and swim about as
active _Colpodoe_.

But this creature is an unmistakable animal, and full-sized _Colpodoe_
may be fed as easily as one feeds chickens. It is only needful to diffuse
very finely ground carmine through the water in which they live, and, in
a very short time, the bodies of the _Colpodoe_ are stuffed with the
deeply- granules of the pigment.

And if this were not sufficient evidence of the animality of _Colpoda_,
there comes the fact that it is even more similar to another well-known
animalcule, _Paramoecium_, than it is to a monad. But _Paramoecium_ is so
huge a creature compared with those hitherto discussed--it reaches 1/120
of an inch or more in length--that there is no difficulty in making out
its organisation in detail; and in proving that it is not only an animal,
but that it is an animal which possesses a somewhat complicated
organisation. For example, the surface layer of its body is different in
structure from the deeper parts. There are two contractile vacuoles, from
each of which radiates a system of vessel-like canals; and not only is
there a conical depression continuous with a tube, which serve as mouth
and gullet, but the food ingested takes a definite course, and refuse is
rejected from a definite region. Nothing is easier than to feed these
animals, and to watch the particles of indigo or carmine accumulate at
the lower end of the gullet. From this they gradually project, surrounded
by a ball of water, which at length passes with a jerk, oddly simulating
a gulp, into the pulpy central substance of the body, there to circulate
up one side and down the other, until its contents are digested and
assimilated. Nevertheless, this complex animal multiplies by division, as
the monad does, and, like the monad, undergoes conjugation. It stands in
the same relation to _Heteromita_ on the animal side, as _Coleochaete_
does on the plant side. Start from either, and such an insensible series
of gradations leads to the monad that it is impossible to say at any
stage of the progress where the line between the animal and the plant
must be drawn.

There is reason to think that certain organisms which pass through a
monad stage of existence, such as the _Myxomycetes_, are, at one time of
their lives, dependent upon external sources for their protein matter, or
are animals; and, at another period, manufacture it, or are plants. And
seeing that the whole progress of modern investigation is in favour of
the doctrine of continuity, it is a fair and probable speculation--though
only a speculation--that, as there are some plants which can manufacture
protein out of such apparently intractable mineral matters as carbonic
acid, water, nitrate of ammonia, metallic and earthy salts; while others
need to be supplied with their carbon and nitrogen in the somewhat less
raw form of tartrate of ammonia and allied compounds; so there may be yet
others, as is possibly the case with the true parasitic plants, which can
only manage to put together materials still better prepared--still more
nearly approximated to protein--until we arrive at such organisms as the
_Psorospermioe_ and the _Panhistophyton_, which are as much animal as
vegetable in structure, but are animal in their dependence on other
organisms for their food.

The singular circumstance observed by Meyer, that the _Torula_ of yeast,
though an indubitable plant, still flourishes most vigorously when
supplied with the complex nitrogenous substance, pepsin; the probability
that the _Peronospora_ is nourished directly by the protoplasm of the
potato-plant; and the wonderful facts which have recently been brought to
light respecting insectivorous plants, all favour this view; and tend to
the conclusion that the difference between animal and plant is one of
degree rather than of kind, and that the problem whether, in a given
case, an organism is an animal or a plant, may be essentially insoluble.



VII


A LOBSTER; OR, THE STUDY OF ZOOLOGY

[1861]

Natural history is the name familiarly applied to the study of the
properties of such natural bodies as minerals, plants, and animals; the
sciences which embody the knowledge man has acquired upon these subjects
are commonly termed Natural Sciences, in contradistinction to other so-
called "physical" sciences; and those who devote themselves especially to
the pursuit of such sciences have been and are commonly termed
"Naturalists."

Linnaeus was a naturalist in this wide sense, and his "Systema Naturae" was
a work upon natural history, in the broadest acceptation of the term; in
it, that great methodising spirit embodied all that was known in his time
of the distinctive characters of minerals, animals, and plants. But the
enormous stimulus which Linnaeus gave to the investigation of nature soon
rendered it impossible that any one man should write another "Systema
Naturae," and extremely difficult for any one to become even a naturalist
such as Linnaeus was.

Great as have been the advances made by all the three branches of
science, of old included under the title of natural history, there can be
no doubt that zoology and botany have grown in an enormously greater
ratio than mineralogy; and hence, as I suppose, the name of "natural
history" has gradually become more and more definitely attached to these
prominent divisions of the subject, and by "naturalist" people have meant
more and more distinctly to imply a student of the structure and function
of living beings.

However this may be, it is certain that the advance of knowledge has
gradually widened the distance between mineralogy and its old associates,
while it has drawn zoology and botany closer together; so that of late
years it has been found convenient (and indeed necessary) to associate
the sciences which deal with vitality and all its phenomena under the
common head of "biology"; and the biologists have come to repudiate any
blood-relationship with their foster-brothers, the mineralogists.

Certain broad laws have a general application throughout both the animal
and the vegetable worlds, but the ground common to these kingdoms of
nature is not of very wide extent, and the multiplicity of details is so
great, that the student of living beings finds himself obliged to devote
his attention exclusively either to the one or the other. If he elects to
study plants, under any aspect, we know at once what to call him. He is a
botanist, and his science is botany. But if the investigation of animal
life be his choice, the name generally applied to him will vary according
to the kind of animals he studies, or the particular phenomena of animal
life to which he confines his attention. If the study of man is his
object, he is called an anatomist, or a physiologist, or an ethnologist;
but if he dissects animals, or examines into the mode in which their
functions are performed, he is a comparative anatomist or comparative
physiologist. If he turns his attention to fossil animals, he is a
palaeontologist. If his mind is more particularly directed to the specific
description, discrimination, classification, and distribution of animals,
he is termed a zoologist.

For the purpose of the present discourse, however, I shall recognise none
of these titles save the last, which I shall employ as the equivalent of
botanist, and I shall use the term zoology is denoting the whole doctrine
of animal life, in contradistinction to botany, which signifies the whole
doctrine of vegetable life.

Employed in this sense, zoology, like botany, is divisible into three
great but subordinate sciences, morphology, physiology, and distribution,
each of which may, to a very great extent, be studied independently of
the other.

Zoological morphology is the doctrine of animal form or structure.
Anatomy is one of its branches; development is another; while
classification is the expression of the relations which different animals
bear to one another, in respect of their anatomy and their development.

Zoological distribution is the study of animals in relation to the
terrestrial conditions which obtain now, or have obtained at any previous
epoch of the earth's history.

Zoological physiology, lastly, is the doctrine of the functions or
actions of animals. It regards animal bodies as machines impelled by
certain forces, and performing an amount of work which can be expressed
in terms of the ordinary forces of nature. The final object of physiology
is to deduce the facts of morphology, on the one hand, and those of
distribution on the other, from the laws of the molecular forces of
matter.

Such is the scope of zoology. But if I were to content myself with the
enunciation of these dry definitions, I should ill exemplify that method
of teaching this branch of physical science, which it is my chief
business to-night to recommend. Let us turn away then from abstract
definitions. Let us take some concrete living thing, some animal, the
commoner the better, and let us see how the application of common sense
and common logic to the obvious facts it presents, inevitably leads us
into all these branches of zoological science.

I have before me a lobster. When I examine it, what appears to be the
most striking character it presents? Why, I observe that this part which
we call the tail of the lobster, is made up of six distinct hard rings
and a seventh terminal piece. If I separate one of the middle rings, say
the third, I find it carries upon its under surface a pair of limbs or
appendages, each of which consists of a stalk and two terminal pieces. So
that I can represent a transverse section of the ring and its appendages
upon the diagram board in this way.

If I now take the fourth ring, I find it has the same structure, and so
have the fifth and the second; so that, in each of these divisions of the
tail, I find parts which correspond with one another, a ring and two
appendages; and in each appendage a stalk and two end pieces. These
corresponding parts are called, in the technical language of anatomy,
"homologous parts." The ring of the third division is the "homologue" of
the ring of the fifth, the appendage of the former is the homologue of
the appendage of the latter. And, as each division exhibits corresponding
parts in corresponding places, we say that all the divisions are
constructed upon the same plan. But now let us consider the sixth
division. It is similar to, and yet different from, the others. The ring
is essentially the same as in the other divisions; but the appendages
look at first as if they were very different; and yet when we regard them
closely, what do we find? A stalk and two terminal divisions, exactly as
in the others, but the stalk is very short and very thick, the terminal
divisions are very broad and flat, and one of them is divided into two
pieces.

I may say, therefore, that the sixth segment is like the others in plan,
but that it is modified in its details.

The first segment is like the others, so far as its ring is concerned,
and though its appendages differ from any of those yet examined in the
simplicity of their structure, parts corresponding with the stem and one
of the divisions of the appendages of the other segments can be readily
discerned in them.

Thus it appears that the lobster's tail is composed of a series of
segments which are fundamentally similar, though each presents peculiar
modifications of the plan common to all. But when I turn to the forepart
of the body I see, at first, nothing but a great shield-like shell,
called technically the "carapace," ending in front in a sharp spine, on
either side of which are the curious compound eyes, set upon the ends of
stout movable stalks. Behind these, on the under side of the body, are
two pairs of long feelers, or antennae, followed by six pairs of jaws
folded against one another over the mouth, and five pairs of legs, the
foremost of these being the great pinchers, or claws, of the lobster.

It looks, at first, a little hopeless to attempt to find in this complex
mass a series of rings, each with its pair of appendages, such as I have
shown you in the abdomen, and yet it is not difficult to demonstrate
their existence. Strip off the legs, and you will find that each pair is
attached to a very definite segment of the under wall of the body; but
these segments, instead of being the lower parts of free rings, as in the
tail, are such parts of rings which are all solidly united and bound
together; and the like is true of the jaws, the feelers, and the eye-
stalks, every pair of which is borne upon its own special segment. Thus
the conclusion is gradually forced upon us, that the body of the lobster
is composed of as many rings as there are pairs of appendages, namely,
twenty in all, but that the six hindmost rings remain free and movable,
while the fourteen front rings become firmly soldered together, their
backs forming one continuous shield--the carapace.

Unity of plan, diversity in execution, is the lesson taught by the study
of the rings of the body, and the same instruction is given still more
emphatically by the appendages. If I examine the outermost jaw I find it
consists of three distinct portions, an inner, a middle, and an outer,
mounted upon a common stem; and if I compare this jaw with the legs
behind it, or the jaws in front of it, I find it quite easy to see, that,
in the legs, it is the part of the appendage which corresponds with the
inner division, which becomes modified into what we know familiarly as
the "leg," while the middle division disappears, and the outer division
is hidden under the carapace. Nor is it more difficult to discern that,
in the appendages of the tail, the middle division appears again and the
outer vanishes; while, on the other hand, in the foremost jaw, the so-
called mandible, the inner division only is left; and, in the same way,
the parts of the feelers and of the eye-stalks can be identified with
those of the legs and jaws.

But whither does all this tend? To the very remarkable conclusion that a
unity of plan, of the same kind as that discoverable in the tail or
abdomen of the lobster, pervades the whole organisation of its skeleton,
so that I can return to the diagram representing any one of the rings of
the tail, which I drew upon the board, and by adding a third division to
each appendage, I can use it as a sort of scheme or plan of any ring of
the body. I can give names to all the parts of that figure, and then if I
take any segment of the body of the lobster, I can point out to you
exactly, what modification the general plan has undergone in that
particular segment; what part has remained movable, and what has become
fixed to another; what has been excessively developed and metamorphosed
and what has been suppressed.

But I imagine I hear the question, How is all this to be tested? No doubt
it is a pretty and ingenious way of looking at the structure of any
animal; but is it anything more? Does Nature acknowledge, in any deeper
way, this unity of plan we seem to trace?

The objection suggested by these questions is a very valid and important
one, and morphology was in an unsound state so long as it rested upon the
mere perception of the analogies which obtain between fully formed parts.
The unchecked ingenuity of speculative anatomists proved itself fully
competent to spin any number of contradictory hypotheses out of the same
facts, and endless morphological dreams threatened to supplant scientific
theory.

Happily, however, there is a criterion of morphological truth, and a sure
test of all homologies. Our lobster has not always been what we see it;
it was once an egg, a semifluid mass of yolk, not so big as a pin's head,
contained in a transparent membrane, and exhibiting not the least trace
of any one of those organs, the multiplicity and complexity of which, in
the adult, are so surprising. After a time, a delicate patch of cellular
membrane appeared upon one face of this yolk, and that patch was the
foundation of the whole creature, the clay out of which it would be
moulded. Gradually investing the yolk, it became subdivided by transverse
constrictions into segments, the forerunners of the rings of the body.
Upon the ventral surface of each of the rings thus sketched out, a pair
of bud-like prominences made their appearance--the rudiments of the
appendages of the ring. At first, all the appendages were alike, but, as
they grew, most of them became distinguished into a stem and two terminal
divisions, to which, in the middle part of the body, was added a third
outer division; and it was only at a later period, that by the
modification, or absorption, of certain of these primitive constituents,
the limbs acquired their perfect form.

Thus the study of development proves that the doctrine of unity of plan
is not merely a fancy, that it is not merely one way of looking at the
matter, but that it is the expression of deep-seated natural facts. The
legs and jaws of the lobster may not merely be regarded as modifications
of a common type,--in fact and in nature they are so,--the leg and the
jaw of the young animal being, at first, indistinguishable.

These are wonderful truths, the more so because the zoologist finds them
to be of universal application. The investigation of a polype, of a
snail, of a fish, of a horse, or of a man, would have led us, though by a
less easy path, perhaps, to exactly the same point. Unity of plan
everywhere lies hidden under the mask of diversity of structure--the
complex is everywhere evolved out of the simple. Every animal has at
first the form of an egg, and every animal and every organic part, in
reaching its adult state, passes through conditions common to other
animals and other adult parts; and this leads me to another point. I have
hitherto spoken as if the lobster were alone in the world, but, as I need
hardly remind you, there are myriads of other animal organisms. Of these,
some, such as men, horses, birds, fishes, snails, slugs, oysters, corals,
and sponges, are not in the least like the lobster. But other animals,
though they may differ a good deal from the lobster, are yet either very
like it, or are like something that is like it. The cray fish, the rock
lobster, and the prawn, and the shrimp, for example, however different,
are yet so like lobsters, that a child would group them as of the lobster
kind, in contradistinction to snails and slugs; and these last again
would form a kind by themselves, in contradistinction to cows, horses,
and sheep, the cattle kind.

But this spontaneous grouping into "kinds" is the first essay of the
human mind at classification, or the calling by a common name of those
things that are alike, and the arranging them in such a manner as best to
suggest the sum of their likenesses and unlikenesses to other things.

Those kinds which include no other subdivisions than the sexes, or
various breeds, are called, in technical language, species. The English
lobster is a species, our cray fish is another, our prawn is another. In
other countries, however, there are lobsters, cray fish, and prawns, very
like ours, and yet presenting sufficient differences to deserve
distinction. Naturalists, therefore, express this resemblance and this
diversity by grouping them as distinct species of the same "genus." But
the lobster and the cray fish, though belonging to distinct genera, have
many features in common, and hence are grouped together in an assemblage
which is called a family. More distant resemblances connect the lobster
with the prawn and the crab, which are expressed by putting all these
into the same order. Again, more remote, but still very definite,
resemblances unite the lobster with the woodlouse, the king crab, the
water flea, and the barnacle, and separate them from all other animals;
whence they collectively constitute the larger group, or class,
_Crustacea_. But the _Crustacea_ exhibit many peculiar features in common
with insects, spiders, and centipedes, so that these are grouped into the
still larger assemblage or "province" _Articulata_; and, finally, the
relations which these have to worms and other lower animals, are
expressed by combining the whole vast aggregate into the sub-kingdom of
_Annulosa_.

If I had worked my way from a sponge instead of a lobster, I should have
found it associated, by like ties, with a great number of other animals
into the sub-kingdom _Protozoa_; if I had selected a fresh-water polype
or a coral, the members of what naturalists term the sub-kingdom
_Coelenterata_, would have grouped themselves around my type; had a snail
been chosen, the inhabitants of all univalve and bivalve, land and water,
shells, the lamp shells, the squids, and the sea-mat would have gradually
linked themselves on to it as members of the same sub-kingdom of
_Mollusca_; and finally, starting from man, I should have been compelled
to admit first, the ape, the rat, the horse, the dog, into the same
class; and then the bird, the crocodile, the turtle, the frog, and the
fish, into the same sub-kingdom of _Vertebrata_.

And if I had followed out all these various lines of classification
fully, I should discover in the end that there was no animal, either
recent or fossil, which did not at once fall into one or other of these
sub-kingdoms. In other words, every animal is organised upon one or other
of the five, or more, plans, the existence of which renders our
classification possible. And so definitely and precisely marked is the
structure of each animal, that, in the present state of our knowledge,
there is not the least evidence to prove that a form, in the slightest
degree transitional between any of the two groups _Vertebrata, Annulosa,
Mollusca_, and _Coelenterata_, either exists, or has existed, during that
period of the earth's history which is recorded by the geologist.[1]
Nevertheless, you must not for a moment suppose, because no such
transitional forms are known, that the members of the sub-kingdoms are
disconnected from, or independent of, one another. On the contrary, in
their earliest condition they are all similar, and the primordial germs
of a man, a dog, a bird, a fish, a beetle, a snail, and a polype are, in
no essential structural respects, distinguishable.

[Footnote 1: The different grouping necessitated by later knowledge does
not affect the principle of the argument.--1894.]

In this broad sense, it may with truth be said, that all living animals,
and all those dead faunae which geology reveals, are bound together by an
all-pervading unity of organisation, of the same character, though not
equal in degree, to that which enables us to discern one and the same
plan amidst the twenty different segments of a lobster's body. Truly it
has been said, that to a clear eye the smallest fact is a window through
which the Infinite may be seen.

Turning from these purely morphological considerations, let us now
examine into the manner in which the attentive study of the lobster
impels us into other lines of research.

Lobsters are found in all the European seas; but on the opposite shores
of the Atlantic and in the seas of the southern hemisphere they do not
exist. They are, however, represented in these regions by very closely
allied, but distinct forms--the _Homarus Americanus_ and the _Homarus
Capensis:_ so that we may say that the European has one species of
_Homuarus_; the American, another; the African, another; and thus the
remarkable facts of geographical distribution begin to dawn upon us.

Again, if we examine the contents of the earth's crust, we shall find in
the latter of those deposits, which have served as the great burying
grounds of past ages, numberless lobster-like animals, but none so
similar to our living lobster as to make zoologists sure that they
belonged even to the same genus. If we go still further back in time, we
discover, in the oldest rocks of all, the remains of animals, constructed
on the same general plan as the lobster, and belonging to the same great
group of _Crustacea_; but for the most part totally different from the
lobster, and indeed from any other living form of crustacean; and thus we
gain a notion of that successive change of the animal population of the
globe, in past ages, which is the most striking fact revealed by geology.

Consider, now, where our inquiries have led us. We studied our type
morphologically, when we determined its anatomy and its development, and
when comparing it, in these respects, with other animals, we made out its
place in a system of classification. If we were to examine every animal
in a similar manner, we should establish a complete body of zoological
morphology.

Again, we investigated the distribution of our type in space and in time,
and, if the like had been done with every animal, the sciences of
geographical and geological distribution would have attained their limit.

But you will observe one remarkable circumstance, that, up to this point,
the question of the life of these organisms has not come under
consideration. Morphology and distribution might be studied almost as
well, if animals and plants were a peculiar kind of crystals, and
possessed none of those functions which distinguish living beings so
remarkably. But the facts of morphology and distribution have to be
accounted for, and the science, the aim of which it is to account for
them, is Physiology.

Let us return to our lobster once more. If we watched the creature in its
native element, we should see it climbing actively the submerged rocks,
among which it delights to live, by means of its strong legs; or swimming
by powerful strokes of its great tail, the appendages of the sixth joint
of which are spread out into a broad fan-like Propeller: seize it, and it
will show you that its great claws are no mean weapons of offence;
suspend a piece of carrion among its haunts, and it will greedily devour
it, tearing and crushing the flesh by means of its multitudinous jaws.

Suppose that we had known nothing of the lobster but as an inert mass, an
organic crystal, if I may use the phrase, and that we could suddenly see
it exerting all these powers, what wonderful new ideas and new questions
would arise in our minds! The great new question would be, "How does all
this take place?" the chief new idea would be, the idea of adaptation to
purpose,--the notion, that the constituents of animal bodies are not mere
unconnected parts, but organs working together to an end. Let us consider
the tail of the lobster again from this point of view. Morphology has
taught us that it is a series of segments composed of homologous parts,
which undergo various modifications--beneath and through which a common
plan of formation is discernible. But if I look at the same part
physiologically, I see that it is a most beautifully constructed organ of
locomotion, by means of which the animal can swiftly propel itself either
backwards or forwards.

But how is this remarkable propulsive machine made to perform its
functions? If I were suddenly to kill one of these animals and to take
out all the soft parts, I should find the shell to be perfectly inert, to
have no more power of moving itself than is possessed by the machinery of
a mill when disconnected from its steam-engine or water-wheel. But if I
were to open it, and take out the viscera only, leaving the white flesh,
I should perceive that the lobster could bend and extend its tail as well
as before. If I were to cut off the tail, I should cease to find any
spontaneous motion in it; but on pinching any portion of the flesh, I
should observe that it underwent a very curious change--each fibre
becoming shorter and thicker. By this act of contraction, as it is
termed, the parts to which the ends of the fibre are attached are, of
course, approximated; and according to the relations of their points of
attachment to the centres of motions of the different rings, the bending
or the extension of the tail results. Close observation of the newly-
opened lobster would soon show that all its movements are due to the same
cause--the shortening and thickening of these fleshy fibres, which are
technically called muscles.

Here, then, is a capital fact. The movements of the lobster are due to
muscular contractility. But why does a muscle contract at one time and
not at another? Why does one whole group of muscles contract when the
lobster wishes to extend his tail, and another group when he desires to
bend it? What is it originates, directs, and controls the motive power?

Experiment, the great instrument for the ascertainment of truth in
physical science, answers this question for us. In the head of the
lobster there lies a small mass of that peculiar tissue which is known as
nervous substance. Cords of similar matter connect his brain of the
lobster, directly or indirectly, with the muscles. Now, if these
communicating cords are cut, the brain remaining entire, the power of
exerting what we call voluntary motion in the parts below the section is
destroyed; and, on the other hand, if, the cords remaining entire, the
brain mass be destroyed, the same voluntary mobility is equally lost.
Whence the inevitable conclusion is, that the power of originating these
motions resides in the brain and is propagated along the nervous cords.

In the higher animals the phenomena which attend this transmission have
been investigated, and the exertion of the peculiar energy which resides
in the nerves has been found to be accompanied by a disturbance of the
electrical state of their molecules.

If we could exactly estimate the signification of this disturbance; if we
could obtain the value of a given exertion of nerve force by determining
the quantity of electricity, or of heat, of which it is the equivalent;
if we could ascertain upon what arrangement, or other condition of the
molecules of matter, the manifestation of the nervous and muscular
energies depends (and doubtless science will some day or other ascertain
these points), physiologists would have attained their ultimate goal in
this direction; they would have determined the relation of the motive
force of animals to the other forms of force found in nature; and if the
same process had been successfully performed for all the operations which
are carried on in, and by, the animal frame, physiology would be perfect,
and the facts of morphology and distribution would be deducible from the
laws which physiologists had established, combined with those determining
the condition of the surrounding universe.

There is not a fragment of the organism of this humble animal whose study
would not lead us into regions of thought as large as those which I have
briefly opened up to you; but what I have been saying, I trust, has not
only enabled you to form a conception of the scope and purport of
zoology, but has given you an imperfect example of the manner in which,
in my opinion, that science, or indeed any physical science, may be best
taught. The great matter is, to make teaching real and practical, by
fixing the attention of the student on particular facts; but at the same
time it should be rendered broad and comprehensive, by constant reference
to the generalisations of which all particular facts are illustrations.
The lobster has served as a type of the whole animal kingdom, and its
anatomy and physiology have illustrated for us some of the greatest
truths of biology. The student who has once seen for himself the facts
which I have described, has had their relations explained to him, and has
clearly comprehended them, has, so far, a knowledge of zoology, which is
real and genuine, however limited it may be, and which is worth more than
all the mere reading knowledge of the science he could ever acquire. His
zoological information is, so far, knowledge and not mere hearsay.

And if it were nay business to fit you for the certificate in zoological
science granted by this department, I should pursue a course precisely
similar in principle to that which I have taken to-night. I should select
a fresh-water sponge, a fresh-water polype or a _Cyanoea_, a fresh-water
mussel, a lobster, a fowl, as types of the five primary divisions of the
animal kingdom. I should explain their structure very fully, and show how
each illustrated the great principles of zoology. Having gone very
carefully and fully over this ground, I should feel that you had a safe
foundation, and I should then take you in the same way, but less
minutely, over similarly selected illustrative types of the classes; and
then I should direct your attention to the special forms enumerated under
the head of types, in this syllabus, and to the other facts there
mentioned.

That would, speaking generally, be my plan. But I have undertaken to
explain to you the best mode of acquiring and communicating a knowledge
of zoology, and you may therefore fairly ask me for a more detailed and
precise account of the manner in which I should propose to furnish you
with the information I refer to.

My own impression is, that the best model for all kinds of training in
physical science is that afforded by the method of teaching anatomy, in
use in the medical schools. This method consists of three elements--
lectures, demonstrations, and examinations.

The object of lectures is, in the first place, to awaken the attention
and excite the enthusiasm of the student; and this, I am sure, may be
effected to a far greater extent by the oral discourse and by the
personal influence of a respected teacher than in any other way.
Secondly, lectures have the double use of guiding the student to the
salient points of a subject, and at the same time forcing him to attend
to the whole of it, and not merely to that part which takes his fancy.
And lastly, lectures afford the student the opportunity of seeking
explanations of those difficulties which will, and indeed ought to, arise
in the course of his studies.

What books shall I read? is a question constantly put by the student to
the teacher. My reply usually is, "None: write your notes out carefully
and fully; strive to understand them thoroughly; come to me for the
explanation of anything you cannot understand; and I would rather you did
not distract your mind by reading." A properly composed course of
lectures ought to contain fully as much matter as a student can
assimilate in the time occupied by its delivery; and the teacher should
always recollect that his business is to feed, and not to cram the
intellect. Indeed, I believe that a student who gains from a course of
lectures the simple habit of concentrating his attention upon a
definitely limited series of facts, until they are thoroughly mastered,
has made a step of immeasurable importance.

But, however good lectures may be, and however extensive the course of
reading by which they are followed up, they are but accessories to the
great instrument of scientific teaching--demonstration. If I insist
unweariedly, nay fanatically, upon the importance of physical science as
an educational agent, it is because the study of any branch of science,
if properly conducted, appears to me to fill up a void left by all other
means of education. I have the greatest respect and love for literature;
nothing would grieve me more than to see literary training other than a
very prominent branch of education: indeed, I wish that real literary
discipline were far more attended to than it is; but I cannot shut my
eyes to the fact, that there is a vast difference between men who have
had a purely literary, and those who have had a sound scientific,
training.

Seeking for the cause of this difference, I imagine I can find it in the
fact that, in the world of letters, learning and knowledge are one, and
books are the source of both; whereas in science, as in life, learning
and knowledge are distinct, and the study of things, and not of books, is
the source of the latter.

All that literature has to bestow may be obtained by reading and by
practical exercise in writing and in speaking; but I do not exaggerate
when I say, that none of the best gifts of science are to be won by these
means. On the contrary, the great benefit which a scientific education
bestows, whether is training or as knowledge, is dependent upon the
extent to which the mind of the student is brought into immediate contact
with facts--upon the degree to which he learns the habit of appealing
directly to Nature, and of acquiring through his senses concrete images
of those properties of things, which are, and always will be, but
approximatively expressed in human language. Our way of looking at
Nature, and of speaking about her, varies from year to year; but a fact
once seen, a relation of cause and effect, once demonstratively
apprehended, are possessions which neither change nor pass away, but, on
the contrary, form fixed centres, about which other truths aggregate by
natural affinity.

Therefore, the great business of the scientific teacher is, to imprint
the fundamental, irrefragable facts of his science, not only by words
upon the mind, but by sensible impressions upon the eye, and ear, and
touch of the student, in so complete a manner, that every term used, or
law enunciated, should afterwards call up vivid images of the particular
structural, or other, facts which furnished the demonstration of the law,
or the illustration of the term.

Now this important operation can only be achieved by constant
demonstration, which may take place to a certain imperfect extent during
a lecture, but which ought also to be carried on independently, and which
should be addressed to each individual student, the teacher endeavouring,
not so much to show a thing to the learner, as to make him see it for
himself.

I am well aware that there are great practical difficulties in the way of
effectual zoological demonstrations. The dissection of animals is not
altogether pleasant, and requires much time; nor is it easy to secure an
adequate supply of the needful specimens. The botanist has here a great
advantage; his specimens are easily obtained, are clean and wholesome,
and can be dissected in a private house as well as anywhere else; and
hence, I believe, the fact, that botany is so much more readily and
better taught than its sister science. But, be it difficult or be it
easy, if zoological science is to be properly studied, demonstration,
and, consequently, dissection, must be had. Without it, no man can have a
really sound knowledge of animal organisation.

A good deal may be done, however, without actual dissection on the
student's part, by demonstration upon specimens and preparations; and in
all probability it would not be very difficult, were the demand
sufficient, to organise collections of such objects, sufficient for all
the purposes of elementary teaching, at a comparatively cheap rate. Even
without these, much might be effected, if the zoological collections,
which are open to the public, were arranged according to what has been
termed the "typical principle"; that is to say, if the specimens exposed
to public view were so selected that the public could learn something
from them, instead of being, as at present, merely confused by their
multiplicity. For example, the grand ornithological gallery at the
British Museum contains between two and three thousand species of birds,
and sometimes five or six specimens of a species. They are very pretty to
look at, and some of the cases are, indeed, splendid; but I will
undertake to say, that no man but a professed ornithologist has ever
gathered much information from the collection. Certainly, no one of the
tens of thousands of the general public who have walked through that
gallery ever knew more about the essential peculiarities of birds when he
left the gallery than when he entered it. But if, somewhere in that vast
hall, there were a few preparations, exemplifying the leading structural
peculiarities and the mode of development of a common fowl; if the types
of the genera, the leading modifications in the skeleton, in the plumage
at various ages, in the mode of nidification, and the like, among birds,
were displayed; and if the other specimens were put away in a place where
the men of science, to whom they are alone useful, could have free access
to them, I can conceive that this collection might become a great
instrument of scientific education.

The last implement of the teacher to which I have adverted is
examination--a means of education now so thoroughly understood that I
need hardly enlarge upon it. I hold that both written and oral
examinations are indispensable, and, by requiring the description of
specimens, they may be made to supplement demonstration.

Such is the fullest reply the time at my disposal will allow me to give
to the question--how may a knowledge of zoology be best acquired and
communicated?

But there is a previous question which may be moved, and which, in fact,
I know many are inclined to move. It is the question, why should teachers
be encouraged to acquire a knowledge of this, or any other branch of
physical science? What is the use, it is said, of attempting to make
physical science a branch of primary education? Is it not probable that
teachers, in pursuing such studies, will be led astray from the
acquirement of more important but less attractive knowledge? And, even if
they can learn something of science without prejudice to their
usefulness, what is the good of their attempting to instil that knowledge
into boys whose real business is the acquisition of reading, writing, and
arithmetic?

These questions are, and will be, very commonly asked, for they arise
from that profound ignorance of the value and true position of physical
science, which infests the minds of the most highly educated and
intelligent classes of the community. But if I did not feel well assured
that they are capable of being easily and satisfactorily answered; that
they have been answered over and over again; and that the time will come
when men of liberal education will blush to raise such questions--I
should be ashamed of my position here to-night. Without doubt, it is your
great and very important function to carry out elementary education;
without question, anything that should interfere with the faithful
fulfilment of that duty on your part would be a great evil; and if I
thought that your acquirement of the elements of physical science, and
your communication of those elements to your pupils, involved any sort of
interference with your proper duties, I should be the first person to
protest against your being encouraged to do anything of the kind.

But is it true that the acquisition of such a knowledge of science as is
proposed, and the communication of that knowledge, are calculated to
weaken your usefulness? Or may I not rather ask, is it possible for you
to discharge your functions properly without these aids?

What is the purpose of primary intellectual education? I apprehend that
its first object is to train the young in the use of those tools
wherewith men extract knowledge from the ever-shifting succession of
phenomena which pass before their eyes; and that its second object is to
inform them of the fundamental laws which have been found by experience
to govern the course of things, so that they may not be turned out into
the world naked, defenceless, and a prey to the events they might
control.

A boy is taught to read his own and other languages, in order that he may
have access to infinitely wider stores of knowledge than could ever be
opened to him by oral intercourse with his fellow men; he learns to
write, that his means of communication with the rest of mankind may be
indefinitely enlarged, and that he may record and store up the knowledge
he acquires. He is taught elementary mathematics, that he may understand
all those relations of number and form, upon which the transactions of
men, associated in complicated societies, are built, and that he may have
some practice in deductive reasoning.

All these operations of reading, writing, and ciphering, are intellectual
tools, whose use should, before all things, be learned, and learned
thoroughly; so that the youth may be enabled to make his life that which
it ought to be, a continual progress in learning and in wisdom.

But, in addition, primary education endeavours to fit a boy out with a
certain equipment of positive knowledge. He is taught the great laws of
morality; the religion of his sect; so much history and geography as will
tell him where the great countries of the world are, what they are, and
how they have become what they are.

Without doubt all these are most fitting and excellent things to teach a
boy; I should be very sorry to omit any of them from any scheme of
primary intellectual education. The system is excellent, so far as it
goes.

But if I regard it closely, a curious reflection arises. I suppose that,
fifteen hundred years ago, the child of any well-to-do Roman citizen was
taught just these same things; reading and writing in his own, and,
perhaps, the Greek tongue; the elements of mathematics; and the religion,
morality, history, and geography current in his time. Furthermore, I do
not think I err in affirming, that, if such a Christian Roman boy, who
had finished his education, could be transplanted into one of our public
schools, and pass through its course of instruction, he would not meet
with a single unfamiliar line of thought; amidst all the new facts he
would have to learn, not one would suggest a different mode of regarding
the universe from that current in his own time.

And yet surely there is some great difference between the civilisation of
the fourth century and that of the nineteenth, and still more between the
intellectual habits and tone of thought of that day and this?

And what has made this difference? I answer fearlessly--The prodigious
development of physical science within the last two centuries.

Modern civilisation rests upon physical science; take away her gifts to
our own country, and our position among the leading nations of the world
is gone to-morrow; for it is physical science only that makes
intelligence and moral energy stronger than brute force.

The whole of modern thought is steeped in science; it has made its way
into the works of our best poets, and even the mere man of letters, who
affects to ignore and despise science, is unconsciously impregnated with
her spirit, and indebted for his best products to her methods. I believe
that the greatest intellectual revolution mankind has yet seen is now
slowly taking place by her agency. She is teaching the world that the
ultimate court of appeal is observation and experiment, and not
authority; she is teaching it to estimate the value of evidence; she is
creating a firm and living faith in the existence of immutable moral and
physical laws, perfect obedience to which is the highest possible aim of
an intelligent being.

But of all this your old stereotyped system of education takes no note.
Physical science, its methods, its problems, and its difficulties, will
meet the poorest boy at every turn, and yet we educate him in such a
manner that he shall enter the world as ignorant of the existence of the
methods and facts of science as the day he was born. The modern world is
full of artillery; and we turn out our children to do battle in it,
equipped with the shield and sword of an ancient gladiator.

Posterity will cry shame on us if we do not remedy this deplorable state
of things. Nay, if we live twenty years longer, our own consciences will
cry shame on us.

It is my firm conviction that the only way to remedy it is to make the
elements of physical science an integral part of primary education. I
have endeavoured to show you how that may be done for that branch of
science which it is my business to pursue; and I can but add, that I
should look upon the day when every schoolmaster throughout this land was
a centre of genuine, however rudimentary, scientific knowledge, as an
epoch in the history of the country.

But let me entreat you to remember my last words. Addressing myself to
you, as teachers, I would say, mere book learning in physical science is
a sham and a delusion--what you teach, unless you wish to be impostors,
that you must first know; and real knowledge in science means personal
acquaintance with the facts, be they few or many.[2]

[Footnote 2: It has been suggested to me that these words may be taken to
imply a discouragement on my part of any sort of scientific instruction
which does not give an acquaintance with the facts at first hand. But
this is not my meaning. The ideal of scientific teaching is, no doubt, a
system by which the scholar sees every fact for himself, and the teacher
supplies only the explanations. Circumstances, however, do not often
allow of the attainment of that ideal, and we must put up with the next
best system--one in which the scholar takes a good deal on trust from a
teacher, who, knowing the facts by his own knowledge, can describe them
with so much vividness as to enable his audience to form competent ideas
concerning them. The system which I repudiate is that which allows
teachers who have not come into direct contact with the leading facts of
a science to pass their second-hand information on. The scientific virus,
like vaccine lymph, if passed through too long a succession of organisms,
will lose all its effect in protecting the young against the intellectual
epidemics to which they are exposed.

[The remarks on p. 222 applied to the Natural History Collection of the
British Museum in 1861. The visitor to the Natural History Museum in 1894
need go no further than the Great Hall to see the realisation of my hopes
by the present Director.]]



VIII


BIOGENESIS AND ABIOGENESIS

(THE PRESIDENTIAL ADDRESS TO THE BRITISH ASSOCIATION FOR THE ADVANCEMENT
OF SCIENCE FOR 1870)

It has long been the custom for the newly installed President of the
British Association for the Advancement of Science to take advantage of
the elevation of the position in which the suffrages of his colleagues
had, for the time, placed him, and, casting his eyes around the horizon
of the scientific world, to report to them what could be seen from his
watch-tower; in what directions the multitudinous divisions of the noble
army of the improvers of natural knowledge were marching; what important
strongholds of the great enemy of us all, ignorance, had been recently
captured; and, also, with due impartiality, to mark where the advanced
posts of science had been driven in, or a long-continued siege had made
no progress.

I propose to endeavour to follow this ancient precedent, in a manner
suited to the limitations of my knowledge and of my capacity. I shall not
presume to attempt a panoramic survey of the world of science, nor even
to give a sketch of what is doing in the one great province of biology,
with some portions of which my ordinary occupations render me familiar.
But I shall endeavour to put before you the history of the rise and
progress of a single biological doctrine; and I shall try to give some
notion of the fruits, both intellectual and practical, which we owe,
directly or indirectly, to the working out, by seven generations of
patient and laborious investigators, of the thought which arose, more
than two centuries ago, in the mind of a sagacious and observant Italian
naturalist.

It is a matter of everyday experience that it is difficult to prevent
many articles of food from becoming covered with mould; that fruit, sound
enough to all appearance, often contains grubs at the core; that meat,
left to itself in the air, is apt to putrefy and swarm with maggots. Even
ordinary water, if allowed to stand in an open vessel, sooner or later
becomes turbid and full of living matter.

The philosophers of antiquity, interrogated as to the cause of these
phenomena, were provided with a ready and a plausible answer. It did not
enter their minds even to doubt that these low forms of life were
generated in the matters in which they made their appearance. Lucretius,
who had drunk deeper of the scientific spirit than any poet of ancient or
modern times except Goethe, intends to speak as a philosopher, rather
than as a poet, when he writes that "with good reason the earth has
gotten the name of mother, since all things are produced out of the
earth. And many living creatures, even now, spring out of the earth,
taking form by the rains and the heat of the sun."[1] The axiom of
ancient science, "that the corruption of one thing is the birth of
another," had its popular embodiment in the notion that a seed dies
before the young plant springs from it; a belief so widespread and so
fixed, that Saint Paul appeals to it in one of the most splendid
outbursts of his fervid eloquence:--

"Thou fool, that which thou sowest is not quickened, except it die."[2]

[Footnote 1: It is thus that Mr. Munro renders

"Linquitur, ut merito maternum nomen adepta
Terra sit, e terra quoniam sunt cuncta creata.
Multaque nunc etiam exsistant animalia terris
Imbribus et calido solis concreta vapore."

_De Rerum Natura_, lib. v. 793-796.

But would not the meaning of the last line be better rendered "Developed
in rain-water and in the warm vapours raised by the sun"?]

[Footnote 2: 1 Corinthians xv. 36.]

The proposition that life may, and does, proceed from that which has no
life, then, was held alike by the philosophers, the poets, and the
people, of the most enlightened nations, eighteen hundred years ago; and
it remained the accepted doctrine of learned and unlearned Europe,
through the Middle Ages, down even to the seventeenth century.

It is commonly counted among the many merits of our great countryman,
Harvey, that he was the first to declare the opposition of fact to
venerable authority in this, as in other matters; but I can discover no
justification for this widespread notion. After careful search through
the "Exercitationes de Generatione," the most that appears clear to me
is, that Harvey believed all animals and plants to spring from what he
terms a "_primordium vegetale_," a phrase which may nowadays be rendered
"a vegetative germ"; and this, he says, is _"oviforme_," or "egg-like";
not, he is careful to add, that it necessarily has the shape of an egg,
but because it has the constitution and nature of one. That this
"_primordium oviforme_" must needs, in all cases, proceed from a living
parent is nowhere expressly maintained by Harvey, though such an opinion
may be thought to be implied in one or two passages; while, on the other
hand, he does, more than once, use language which is consistent only with
a full belief in spontaneous or equivocal generation.[3] In fact, the
main concern of Harvey's wonderful little treatise is not with
generation, in the physiological sense, at all, but with development; and
his great object is the establishment of the doctrine of epigenesis.

[Footnote 3: See the following passage in Exercitatio I.:--"Item _sponte
nascentia_ dicuntur; non quod ex _putredine_ oriunda sint, sed quod casu,
naturae sponte, et aequivoca (ut aiunt) generatione, a parentibus sui
dissimilibus proveniant." Again, in _De Uteri Membranis:_--"In cunctorum
viventium generatione (sicut diximus) hoc solenne est, ut ortum ducunt a
_primordio_ aliquo, quod tum materiam tum elficiendi potestatem in se
habet: sitque, adeo id, ex quo et a quo quicquid nascitur, ortum suum
ducat. Tale primordium in animalibus (_sive ab aliis generantibus
proveniant, sive sponte, aut ex putredine nascentur_) est humor in
tunica, aliquaaut putami ne conclusus." Compare also what Redi has to say
respecting Harvey's opinions, _Esperienze_, p. 11.]

The first distinct enunciation of the hypothesis that all living matter
has sprung from pre-existing living matter, came from a contemporary,
though a junior, of Harvey, a native of that country, fertile in men
great in all departments of human activity, which was to intellectual
Europe, in the sixteenth and seventeenth centuries, what Germany is in
the nineteenth. It was in Italy, and from Italian teachers, that Harvey
received the most important part of his scientific education. And it was
a student trained in the same schools, Francesco Redi--a man of the
widest knowledge and most versatile abilities, distinguished alike as
scholar, poet, physician, and naturalist--who, just two hundred and two
years ago, published his "Esperienze intorno alla Generazione degl'
Insetti," and gave to the world the idea, the growth of which it is my
purpose to trace. Redi's book went through five editions in twenty years;
and the extreme simplicity of his experiments, and the clearness of his
arguments, gained for his views, and for their consequences, almost
universal acceptance.

Redi did not trouble himself much with speculative considerations, but
attacked particular cases of what was supposed to be "spontaneous
generation" experimentally. Here are dead animals, or pieces of meat,
says he; I expose them to the air in hot weather, and in a few days they
swarm with maggots. You tell me that these are generated in the dead
flesh; but if I put similar bodies, while quite fresh, into a jar, and
tie some fine gauze over the top of the jar, not a maggot makes its
appearance, while the dead substances, nevertheless, putrefy just in the
same way as before. It is obvious, therefore, that the maggots are not
generated by the corruption of the meat; and that the cause of their
formation must be a something which is kept away by gauze. But gauze will
not keep away aeriform bodies, or fluids. This something must, therefore,
exist in the form of solid particles too big to get through the gauze.
Nor is one long left in doubt what these solid particles are; for the
blowflies, attracted by the odour of the meat, swarm round the vessel,
and, urged by a powerful but in this case misleading instinct, lay eggs
out of which maggots are immediately hatched, upon the gauze. The
conclusion, therefore, is unavoidable; the maggots are not generated by
the meat, but the eggs which give rise to them are brought through the
air by the flies.

These experiments seem almost childishly simple, and one wonders how it
was that no one ever thought of them before. Simple as they are, however,
they are worthy of the most careful study, for every piece of
experimental work since done, in regard to this subject, has been shaped
upon the model furnished by the Italian philosopher. As the results of
his experiments were the same, however varied the nature of the materials
he used, it is not wonderful that there arose in Redi's mind a
presumption, that, in all such cases of the seeming production of life
from dead matter, the real explanation was the introduction of living
germs from without into that dead matter.[4] And thus the hypothesis that
living matter always arises by the agency of pre-existing living matter,
took definite shape; and had, henceforward, a right to be considered and
a claim to be refuted, in each particular case, before the production of
living matter in any other way could be admitted by careful reasoners. It
will be necessary for me to refer to this hypothesis so frequently, that,
to save circumlocution, I shall call it the hypothesis of _Biogenesis_;
and I shall term the contrary doctrine--that living matter may be
produced by not living matter--the hypothesis of _Abiogenesis_.

[Footnote 4: "Pure contentandomi sempre in questa ed in ciascuna altro
cosa, da ciascuno piu savio, la dove io difettuosamente parlassi, esser
corretto; non tacero, che per molte osservazioni molti volti da me fatte,
mi sento inclinato a credere che la terra, da quelle prime piante, e da
quei primi animali in poi, che ella nei primi giorni del mondo produsse
per comandemento del sovrano ed omnipotente Fattore, non abbia mai piu
prodotto da se medesima ne erba ne albero, ne animale alcuno perfetto o
imperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassati
e nato e che ora nascere in lei, o da lei veggiamo, venga tutto dalla
semenza reale e vera delle piante, e degli animali stessi, i quali col
mezzo del proprio seme la loro spezie conservano. E se bene tutto giorno
scorghiamo da' cadaveri degli animali, e da tutte quante le maniere dell'
erbe, e de' fiori, e dei frutti imputriditi, e corrotti nascere vermi
infiniti--

'Nonne vides quaecunque mora, fluidoque calore
Corpora tabescunt in parva animalia verti'--

Io mi sento, dico, inclinato, a credere che tutti quei vermi si generino
dal seme paterno; e che le carni, e l' erbe, e l' altre cose tutte
putrefatte, o putrefattibili non facciano altra parte, ne abbiano altro
ufizio nella generazione degl' insetti, se non d'apprestare un luogo o un
nido proporzionato, in cui dagli animali nel tempo della figliatura sieno
portati, e partoriti i vermi, o l' uova o l' altre semenze dei vermi, i
quali tosto che nati sono, trovano in esso nido un sufficiente alimento
abilissimo per nutricarsi: e se in quello non son portate dalle madri
queste suddette semenze, niente mai, e replicatamente niente, vi s'
ingegneri e nasca."--REDI, _Esperienze_, pp. 14-16.]

In the seventeenth century, as I have said, the latter was the dominant
view, sanctioned alike by antiquity and by authority; and it is
interesting to observe that Redi did not escape the customary tax upon a
discoverer of having to defend himself against the charge of impugning
the authority of the Scriptures;[5] for his adversaries declared that the
generation of bees from the carcase of a dead lion is affirmed, in the
Book of Judges, to have been the origin of the famous riddle with which
Samson perplexed the Philistines:--

Out of the eater came forth meat,
And out of the strong came forth sweetness.

[Footnote 5: "Molti, e molti altri ancora vi potrei annoverare, se non
fossi chiamato a rispondere alle rampogne di alcuni, che bruscamente mi
rammentano cio, che si legge nel capitolo quattordicesimo del sacrosanto
Libro de' giudici ... "--REDI, _loc. cit._ p. 45.]

Against all odds, however, Redi, strong with the strength of demonstrable
fact, did splendid battle for Biogenesis; but it is remarkable that he
held the doctrine in a sense which, if he lead lived in these times,
would have infallibly caused him to be classed among the defenders of
"spontaneous generation." "Omne vivum ex vivo," "no life without
antecedent life," aphoristically sums up Redi's doctrine; but he went no
further. It is most remarkable evidence of the philosophic caution and
impartiality of his mind, that although he had speculatively anticipated
the manner in which grubs really are deposited in fruits and in the galls
of plants, he deliberately admits that the evidence is insufficient to
bear him out; and he therefore prefers the supposition that they are
generated by a modification of the living substance of the plants
themselves. Indeed, he regards these vegetable growths as organs, by
means of which the plant gives rise to an animal, and looks upon this
production of specific animals as the final cause of the galls and of, at
any rate, some fruits. And he proposes to explain the occurrence of
parasites within the animal body in the same way.[6]

[Footnote 6: The passage (_Esperienze_, p. 129) is worth quoting in
full:--

"Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi,
gli alberi e le foglie, in due maniere inverminassero. Una, perche
venendo i bachi per di fuora, e cercando l' alimento, col rodere ci
aprono la strada, ed arrivano alla piu interna midolla de' frutti e de'
legni. L'altra maniera si e, che io per me stimerei, che non fosse gran
fatto disdicevole il credere, che quell' anima o quella virtu, la quale
genera i fiori ed i frutti nelle piante viventi, sia quella stessa che
generi ancora i bachi di esse piante. E chi sa, forse, che molti frutti
degli alberi non sieno prodotti, non per un fine primario e principale,
ma bensi per un uffizio secondario e servile, destinato alla generazione
di que' vermi, servendo a loro in vece di matrice, in cui dimorino un
prefisso e determinato tempo; il quale arrivato escan fuora a godere il
sole.

"Io m' immagino, che questo mio pensiero non vi parra totalmento un
paradosso; mentro farete riflessione a quelle tanto sorte di galle, di
gallozzole, di coccole, di ricci, di calici, di cornetti ed i lappole,
che son produtte dalle quercel, dalle farnie, da' cerri, da' sugheri, da'
leeci e da altri simili alberi de ghianda; imperciocche in quello
gallozzole, e particolarmente nelle piu grosse, che si chiamano coronati,
ne' ricci capelluti, che ciuffoli da' nostri contadini son detti; nei
ricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzze
della foglia del leccio si vede evidentissimamente, che la prima e
principale intenzione della natura e formare dentro di quelle un animale
volante; vedendosi nel centro della gallozzola un uovo, che col crescere
e col maturarsi di essa gallozzola va crescendo e maturando anch' egli, e
cresce altresi a suo tempo quel verme, che nell' uovo si racchiude; il
qual verme, quando la gallozzola e finita di maturare e che e venuto il
termine destinato al suo nascimento, diventa, di verme che era, una
mosca.... Io vi confesso ingenuamente, che prima d'aver fatte queste mie
esperienze intorno alla generazione degl' insetti mi dava a credere, o
per dir meglio sospettava, che forse la gallozzola nascesse, perche
arrivando la mosca nel tempo della primavera, e facendo una piccolissima
fessura ne' rami piu teneri della quercia, in quella fessura nascondesse
uno de suoi semi, il quale fosse cagione che sbocciasse fuora la
gallozzola; e che mai non si vedessero galle o gallozzole o ricci o
cornetti o calici o coccole, se non in que' rami, ne' quali le mosche
avessero depositate le loro semenze; e mi dava ad intendere, che le
gallozzole fossero una malattia cagionata nelle querce dalle punture
delle mosche, in quella giusa stessa che dalle punture d'altri animaletti
simiglievoli veggiamo crescere de' tumori ne' corpi degli animali."]

It is of great importance to apprehend Redi's position rightly; for the
lines of thought he laid down for us are those upon which naturalists
have been working ever since. Clearly, he held _Biogenesis_ as against
_Abiogenesis;_ and I shall immediately proceed, in the first place, to
inquire how far subsequent investigation has borne him out in so doing.

But Redi also thought that there were two modes of Biogenesis. By the one
method, which is that of common and ordinary occurrence, the living
parent gives rise to offspring which passes through the same cycle of
changes as itself--like gives rise to like; and this has been termed
_Homogenesis_. By the other mode, the living parent was supposed to give
rise to offspring which passed through a totally different series of
states from those exhibited by the parent, and did not return into the
cycle of the parent; this is what ought to be called _Heterogenesis_, the
offspring being altogether, and permanently, unlike the parent. The term
Heterogenesis, however, has unfortunately been used in a different sense,
and M. Milne-Edwards has therefore substituted for it _Xenogenesis_,
which means the generation of something foreign. After discussing Redi's
hypothesis of universal Biogenesis, then, I shall go on to ask how far
the growth of science justifies his other hypothesis of Xenogenesis.

The progress of the hypothesis of Biogenesis was triumphant and unchecked
for nearly a century. The application of the microscope to anatomy in the
hands of Grew, Leeuwenhoek, Swammerdam, Lyonnet, Vallisnieri, Reaurnur,
and other illustrious investigators of nature of that day, displayed such
a complexity of organisation in the lowest and minutest forms, and
everywhere revealed such a prodigality of provision for their
multiplication by germs of one sort or another, that the hypothesis of
Abiogenesis began to appear not only untrue, but absurd; and, in the
middle of the eighteenth century, when Needham and Buffon took up the
question, it was almost universally discredited.[7]

[Footnote 7: Needham, writing in 1750, says:--

"Les naturalistes modernes s'accordent unaninement a etablir, comme une
verite certaine, que toute plante vient do sa semence specifique, tout
animal d'un oeuf ou de quelque chose d'analogue preexistant dans la
plante, ou dans l'animal de meme espece qui l'a produit."--_Nouvelles
Observations_, p. 169.

"Les naturalistes out generalemente cru que les animaux microscopiques
etaient engendres par des oeufs transportes dans l'air, ou deposes dans
des eaux dormantes par des insectes volans."--_Ibid._ p. 176.]

But the skill of the microscope makers of the eighteenth century soon
reached its limit. A microscope magnifying 400 diameters was a _chef
d'oeuvre_ of the opticians of that day; and, at the same time, by no
means trustworthy. But a magnifying power of 400 diameters, even when
definition reaches the exquisite perfection of our modern achromatic
lenses, hardly suffices for the mere discernment of the smallest forms of
life. A speck, only 1/25th of an inch in diameter, has, at ten inches
from the eye, the same apparent size as an object 1/10000th of an inch in
diameter, when magnified 400 times; but forms of living matter abound,
the diameter of which is not more than 1/40000th of an inch. A filtered
infusion of hay, allowed to stand for two days, will swarm with living
things among which, any which reaches the diameter of a human red blood-
corpuscle, or about 1/3200th of an inch, is a giant. It is only by
bearing these facts in mind, that we can deal fairly with the remarkable
statements and speculations put forward by Buffon and Needham in the
middle of the eighteenth century.

When a portion of any animal or vegetable body is infused in water, it
gradually softens and disintegrates; and, as it does so, the water is
found to swarm with minute active creatures, the so-called Infusorial
Animalcules, none of which can be seen, except by the aid of the
microscope; while a large proportion belong to the category of smallest
things of which I have spoken, and which must have looked like mere dots
and lines under the ordinary microscopes of the eighteenth century.

Led by various theoretical considerations which I cannot now discuss, but
which looked promising enough in the lights of their time, Buffon and
Needham doubted the applicability of Redi's hypothesis to the infusorial
animalcules, and Needham very properly endeavoured to put the question to
an experimental test. He said to himself, If these infusorial animalcules
come from germs, their germs must exist either in the substance infused,
or in the water with which the infusion is made, or in the superjacent
air. Now the vitality of all germs is destroyed by heat. Therefore, if I
boil the infusion, cork it up carefully, cementing the cork over with
mastic, and then heat the whole vessel by heaping hot ashes over it, I
must needs kill whatever germs are present. Consequently, if Redi's
hypothesis hold good, when the infusion is taken away and allowed to
cool, no animalcules ought to be developed in it; whereas, if the
animalcules are not dependent on pre-existing germs, but are generated
from the infused substance, they ought, by and by, to make their
appearance. Needham found that, under the circumstances in which he made
his experiments, animalcules always did arise in the infusions, when a
sufficient time had elapsed to allow for their development.

In much of his work Needham was associated with Buffon, and the results
of their experiments fitted in admirably with the great French
naturalist's hypothesis of "organic molecules," according to which, life
is the indefeasible property of certain indestructible molecules of
matter, which exist in all living things, and have inherent activities by
which they are distinguished from not living matter. Each individual
living organism is formed by their temporary combination. They stand to
it in the relation of the particles of water to a cascade, or a
whirlpool; or to a mould, into which the water is poured. The form of the
organism is thus determined by the reaction between external conditions
and the inherent activities of the organic molecules of which it is
composed; and, as the stoppage of a whirlpool destroys nothing but a
form, and leaves the molecules of the water, with all their inherent
activities intact, so what we call the death and putrefaction of an
animal, or of a plant, is merely the breaking up of the form, or manner
of association, of its constituent organic molecules, which are then set
free as infusorial animalcules.

It will be perceived that this doctrine is by no means identical with
_Abiogenesis_, with which it is often confounded. On this hypothesis, a
piece of beef, or a handful of hay, is dead only in a limited sense. The
beef is dead ox, and the hay is dead grass; but the "organic molecules"
of the beef or the hay are not dead, but are ready to manifest their
vitality as soon as the bovine or herbaceous shrouds in which they are
imprisoned are rent by the macerating action of water. The hypothesis
therefore must be classified under Xenogenesis, rather than under
Abiogenesis. Such as it was, I think it will appear, to those who will be
just enough to remember that it was propounded before the birth of modern
chemistry, and of the modern optical arts, to be a most ingenious and
suggestive speculation.

But the great tragedy of Science--the slaying of a beautiful hypothesis
by an ugly fact--which is so constantly being enacted under the eyes of
philosophers, was played, almost immediately, for the benefit of Buffon
and Needham.

Once more, an Italian, the Abbe Spallanzani, a worthy successor and
representative of Redi in his acuteness, his ingenuity, and his learning,
subjected the experiments and the conclusions of Needham to a searching
criticism. It might be true that Needham's experiments yielded results
such as he had described, but did they bear out his arguments? Was it not
possible, in the first place, he had not completely excluded the air by
his corks and mastic? And was it not possible, in the second place, that
he had not sufficiently heated his infusions and the superjacent air?
Spallanzani joined issue with the English naturalist on both these pleas,
and he showed that if, in the first place, the glass vessels in which the
infusions were contained were hermetically sealed by fusing their necks,
and if, in the second place, they were exposed to the temperature of
boiling water for three-quarters of an hour,[8] no animalcules ever made
their appearance within them. It must be admitted that the experiments
and arguments of Spallanzani furnish a complete and a crushing reply to
those of Needham. But we all too often forget that it is one thing to
refute a proposition, and another to prove the truth of a doctrine which,
implicitly or explicitly, contradicts that proposition; and the advance
of science soon showed that though Needham might be quite wrong, it did
not follow that Spallanzani was quite right.

[Footnote 8: See Spallanzani, _Opere_, vi. pp. 42 and 51.]

Modern Chemistry, the birth of the latter half of the eighteenth century,
grew apace, and soon found herself face to face with the great problems
which biology had vainly tried to attack without her help. The discovery
of oxygen led to the laying of the foundations of a scientific theory of
respiration, and to an examination of the marvellous interactions of
organic substances with oxygen. The presence of free oxygen appeared to
be one of the conditions of the existence of life, and of those singular
changes in organic matters which are known as fermentation and
putrefaction. The question of the generation of the infusory animalcules
thus passed into a new phase. For what might not have happened to the
organic matter of the infusions, or to the oxygen of the air, in
Spallanzani's experiments? What security was there that the development
of life which ought to have taken place had not been checked or prevented
by these changes?

The battle had to be fought again. It was needful to repeat the
experiments under conditions which would make sure that neither the
oxygen of the air, nor the composition of the organic matter, was altered
in such a manner as to interfere with the existence of life.

Schulze and Schwann took up the question from this point of view in 1836
and 1837. The passage of air through red-hot glass tubes, or through
strong sulphuric acid, does not alter the proportion of its oxygen, while
it must needs arrest, or destroy, any organic matter which may be
contained in the air. These experimenters, therefore, contrived
arrangements by which the only air which should come into contact with a
boiled infusion should be such as had either passed through red-hot tubes
or through strong sulphuric acid. The result which they obtained was that
an infusion so treated developed no living things, while, if the same
infusion was afterwards exposed to the air, such things appeared rapidly
and abundantly. The accuracy of these experiments has been alternately
denied and affirmed. Supposing then, to be accepted, however, all that
they really proved was that the treatment to which the air was subjected
destroyed _something_ that was essential to the development of life in
the infusion. This "something" might be gaseous, fluid, or solid; that it
consisted of germs remained only an hypothesis of greater or less
probability.

Contemporaneously with these investigations a remarkable discovery was
made by Cagniard de la Tour. He found that common yeast is composed of a
vast accumulation of minute plants. The fermentation of must, or of wort,
in the fabrication of wine and of beer, is always accompanied by the
rapid growth and multiplication of these _Toruloe_. Thus, fermentation,
in so far as it was accompanied by the development of microscopical
organisms in enormous numbers, became assimilated to the decomposition of
an infusion of ordinary animal or vegetable matter; and it was an obvious
suggestion that the organisms were, in some way or other, the causes both
of fermentation and of putrefaction. The chemists, with Berzelius and
Liebig at their head, at first laughed this idea to scorn; but in 1843, a
man then very young, who has since performed the unexampled feat of
attaining to high eminence alike in Mathematics, Physics, and Physiology--
I speak of the illustrious Helmholtz--reduced the matter to the test of
experiment by a method alike elegant and conclusive. Helmholtz separated
a putrefying or a fermenting liquid from one which was simply putrescible
or fermentable by a membrane which allowed the fluids to pass through and
become intermixed, but stopped the passage of solids. The result was,
that while the putrescible or the fermentable liquids became impregnated
with the results of the putrescence or fermentation which was going on on
the other side of the membrane, they neither putrefied (in the ordinary
way) nor fermented; nor were any of the organisms which abounded in the
fermenting or putrefying liquid generated in them. Therefore the cause of
the development of these organisms must lie in something which cannot
pass through membranes; and as Helmholtz's investigations were long
antecedent to Graham's researches upon colloids, his natural conclusion
was that the agent thus intercepted must be a solid material. In point of
fact, Helmholtz's experiments narrowed the issue to this: that which
excites fermentation and putrefaction, and at the same time gives rise to
living forms in a fermentable or putrescible fluid, is not a gas and is
not a diffusible fluid; therefore it is either a colloid, or it is matter
divided into very minute solid particles.

The researches of Schroeder and Dusch in 1854, and of Schroeder alone, in
1859, cleared up this point by experiments which are simply refinements
upon those of Redi. A lump of cotton-wool is, physically speaking, a pile
of many thicknesses of a very fine gauze, the fineness of the meshes of
which depends upon the closeness of the compression of the wool. Now,
Schroeder and Dusch found, that, in the case of all the putrefiable
materials which they used (except milk and yolk of egg), an infusion
boiled, and then allowed to come into contact with no air but such as had
been filtered through cotton-wool, neither putrefied, nor fermented, nor
developed living forms. It is hard to imagine what the fine sieve formed
by the cotton-wool could have stopped except minute solid particles.
Still the evidence was incomplete until it had been positively shown,
first, that ordinary air does contain such particles; and, secondly, that
filtration through cotton-wool arrests these particles and allows only
physically pure air to pass. This demonstration has been furnished within
the last year by the remarkable experiments of Professor Tyndall. It has
been a common objection of Abiogenists that, if the doctrine of Biogeny
is true, the air must be thick with germs; and they regard this as the
height of absurdity. But nature occasionally is exceedingly unreasonable,
and Professor Tyndall has proved that this particular absurdity may
nevertheless be a reality. He has demonstrated that ordinary air is no
better than a sort of stirabout of excessively minute solid particles;
that these particles are almost wholly destructible by heat; and that
they are strained off, and the air rendered optically pure, by its being
passed through cotton-wool.

It remains yet in the order of logic, though not of history, to show that
among these solid destructible particles, there really do exist germs
capable of giving rise to the development of living forms in suitable
menstrua. This piece of work was done by M. Pasteur in those beautiful
researches which will ever render his name famous; and which, in spite of
all attacks upon them, appear to me now, as they did seven years ago,[9]
to be models of accurate experimentation and logical reasoning. He
strained air through cotton-wool, and found, as Schroeder and Dusch had
done, that it contained nothing competent to give rise to the development
of life in fluids highly fitted for that purpose. But the important
further links in the chain of evidence added by Pasteur are three. In the
first place he subjected to microscopic examination the cotton-wool which
had served as strainer, and found that sundry bodies clearly recognisable
as germs, were among the solid particles strained off. Secondly, he
proved that these germs were competent to give rise to living forms by
simply sowing them in a solution fitted for their development. And,
thirdly, he showed that the incapacity of air strained through cotton-
wool to give rise to life, was not due to any occult change effected in
the constituents of the air by the wool, by proving that the cotton-wool
might be dispensed with altogether, and perfectly free access left
between the exterior air and that in the experimental flask. If the neck
of the flask is drawn out into a tube and bent downwards; and if, after
the contained fluid has been carefully boiled, the tube is heated
sufficiently to destroy any germs which may be present in the air which
enters as the fluid cools, the apparatus may be left to itself for any
time and no life will appear in the fluid. The reason is plain. Although
there is free communication between the atmosphere laden with germs and
the germless air in the flask, contact between the two takes place only
in the tube; and as the germs cannot fall upwards, and there are no
currents, they never reach the interior of the flask. But if the tube be
broken short off where it proceeds from the flask, and free access be
thus given to germs falling vertically out of the air, the fluid, which
has remained clear and desert for months, becomes, in a few days, turbid
and full of life.

[Footnote 9: _Lectures to Working Men on the Causes of the Phenomena of
Organic Nature_, 1863. (See Vol. II. of these Essays.)]

These experiments have been repeated over and over again by independent
observers with entire success; and there is one very simple mode of
seeing the facts for one's self, which I may as well describe.

Prepare a solution (much used by M. Pasteur, and often called "Pasteur's
solution") composed of water with tartrate of ammonia, sugar, and yeast-
ash dissolved therein.[10] Divide it into three portions in as many
flasks; boil all three for a quarter of an hour; and, while the steam is
passing out, stop the neck of one with a large plug of cotton-wool, so
that this also may be thoroughly steamed. Now set the flasks aside to
cool, and, when their contents are cold, add to one of the open ones a
drop of filtered infusion of hay which has stood for twenty-four hours,
and is consequently hill of the active and excessively minute organisms
known as _Bacteria_. In a couple of days of ordinary warm weather the
contents of this flask will be milky from the enormous multiplication of
_Bacteria_. The other flask, open and exposed to the air, will, sooner or
later, become milky with _Bacteria_, and patches of mould may appear in
it; while the liquid in the flask, the neck of which is plugged with
cotton-wool, will remain clear for an indefinite time. I have sought in
vain for any explanation of these facts, except the obvious one, that the
air contains germs competent to give rise to _Bacteria_, such as those
with which the first solution has been knowingly and purposely
inoculated, and to the mould-_Fungi_. And I have not yet been able to
meet with any advocate of Abiogenesis who seriously maintains that the
atoms of sugar, tartrate of ammonia, yeast-ash, and water, under no
influence but that of free access of air and the ordinary temperature,
re-arrange themselves and give rise to the protoplasm of _Bacterium_. But
the alternative is to admit that these _Bacteria_ arise from germs in the
air; and if they are thus propagated, the burden of proof that other like
forms are generated in a different manner, must rest with the assertor of
that proposition.

[Footnote 10: Infusion of hay treated in the same way yields similar
results; but as it contains organic matter, the argument which follows
cannot be based upon it.]

To sum up the effect of this long chain of evidence:--

It is demonstrable that a fluid eminently fit for the development of the
lowest forms of life, but which contains neither germs, nor any protein
compound, gives rise to living things in great abundance if it is exposed
to ordinary air; while no such development takes place, if the air with
which it is in contact is mechanically freed from the solid particles
which ordinarily float in it, and which may be made visible by
appropriate means.

It is demonstrable that the great majority of these particles are
destructible by heat, and that some of them are germs, or living
particles, capable of giving rise to the same forms of life as those
which appear when the fluid is exposed to unpurified air.

It is demonstrable that inoculation of the experimental fluid with a drop
of liquid known to contain living particles gives rise to the same
phenomena as exposure to unpurified air.

And it is further certain that these living particles are so minute that
the assumption of their suspension in ordinary air presents not the
slightest difficulty. On the contrary, considering their lightness and
the wide diffusion of the organisms which produce them, it is impossible
to conceive that they should not be suspended in the atmosphere in
myriads.

Thus the evidence, direct and indirect, in favour of _Biogenesis_ for all
known forms of life must, I think, be admitted to be of great weight.

On the other side, the sole assertions worthy of attention are that
hermetically sealed fluids, which have been exposed to great and long-
continued heat, have sometimes exhibited living forms of low organisation
when they have been opened.

The first reply that suggests itself is the probability that there must
be some error about these experiments, because they are performed on an
enormous scale every day with quite contrary results. Meat, fruits,
vegetables, the very materials of the most fermentable and putrescible
infusions, are preserved to the extent, I suppose I may say, of thousands
of tons every year, by a method which is a mere application of
Spallanzani's experiment. The matters to be preserved are well boiled in
a tin case provided with a small hole, and this hole is soldered up when
all the air in the case has been replaced by steam. By this method they
may be kept for years without putrefying, fermenting, or getting mouldy.
Now this is not because oxygen is excluded, inasmuch as it is now proved
that free oxygen is not necessary for either fermentation or
putrefaction. It is not because the tins are exhausted of air, for
_Vibriones_ and _Bacteria_ live, as Pasteur has shown, without air or
free oxygen. It is not because the boiled meats or vegetables are not
putrescible or fermentable, as those who have had the misfortune to be in
a ship supplied with unskilfully closed tins well know. What is it,
therefore, but the exclusion of germs? I think that Abiogenists are bound
to answer this question before they ask us to consider new experiments of
precisely the same order.

And in the next place, if the results of the experiments I refer to are
really trustworthy, it by no means follows that Abiogenesis has taken
place. The resistance of living matter to heat is known to vary within
considerable limits, and to depend, to some extent, upon the chemical and
physical qualities of the surrounding medium. But if, in the present
state of science, the alternative is offered us,--either germs can stand
a greater heat than has been supposed, or the molecules of dead matter,
for no valid or intelligible reason that is assigned, are able to re-
arrange themselves into living bodies, exactly such as can be
demonstrated to be frequently produced in another way,--I cannot
understand how choice can be, even for a moment, doubtful.

But though I cannot express this conviction of mine too strongly, I must
carefully guard myself against the supposition that I intend to suggest
that no such thing as Abiogenesis ever has taken place in the past, or
ever will take place in the future. With organic chemistry, molecular
physics, and physiology yet in their infancy, and every day making
prodigious strides, I think it would be the height of presumption for any
man to say that the conditions under which matter assumes the properties
we call "vital" may not, some day, be artificially brought together. All
I feel justified in affirming is, that I see no reason for believing that
the feat has been performed yet.

And looking back through the prodigious vista of the past, I find no
record of the commencement of life, and therefore I am devoid of any
means of forming a definite conclusion as to the conditions of its
appearance. Belief, in the scientific sense of the word, is a serious
matter, and needs strong foundations. To say, therefore, in the admitted
absence of evidence, that I have any belief as to the mode in which the
existing forms of life have originated, would be using words in a wrong
sense. But expectation is permissible where belief is not; and if it were
given me to look beyond the abyss of geologically recorded time to the
still more remote period when the earth was passing through physical and
chemical conditions, which it can no more see again than a man can recall
his infancy, I should expect to be a witness of the evolution of living
protoplasm from not living matter. I should expect to see it appear under
forms of great simplicity, endowed, like existing fungi, with the power
of determining the formation of new protoplasm from such matters as
ammonium carbonates, oxalates and tartrates, alkaline and earthy
phosphates, and water, without the aid of light. That is the expectation
to which analogical reasoning leads me; but I beg you once more to
recollect that I have no right to call my opinion anything but an act of
philosophical faith.

So much for the history of the progress of Redi's great doctrine of
Biogenesis, which appears to me, with the limitations I have expressed,
to be victorious along the whole line at the present day.

As regards the second problem offered to us by Redi, whether Xenogenesis
obtains, side by side with Homogenesis,--whether, that is, there exist
not only the ordinary living things, giving rise to offspring which run
through the same cycle as themselves, but also others, producing
offspring which are of a totally different character from themselves,--
the researches of two centuries have led to a different result. That the
grubs found in galls are no product of the plants on which the galls
grow, but are the result of the introduction of the eggs of insects into
the substance of these plants, was made out by Vallisnieri, Reaumur, and
others, before the end of the first half of the eighteenth century. The
tapeworms, bladderworms, and flukes continued to be a stronghold of the
advocates of Xenogenesis for a much longer period. Indeed, it is only
within the last thirty years that the splendid patience of Von Siebold,
Van Beneden, Leuckart, Kuechenmeister, and other helminthologists, has
succeeded in tracing every such parasite, often through the strangest
wanderings and metamorphoses, to an egg derived from a parent, actually
or potentially like itself; and the tendency of inquiries elsewhere has
all been in the same direction. A plant may throw off bulbs, but these,
sooner or later, give rise to seeds or spores, which develop into the
original form. A polype may give rise to Medusae, or a pluteus to an
Echinoderm, but the Medusa and the Echinoderm give rise to eggs which
produce polypes or glutei, and they are therefore only stages in the
cycle of life of the species.

But if we turn to pathology, it offers us some remarkable approximations
to true Xenogenesis.

As I have already mentioned, it has been known since the time of
Vallisnieri and of Reaumur, that galls in plants, and tumours in cattle,
are caused by insects, which lay their eggs in those parts of the animal
or vegetable frame of which these morbid structures are outgrowths.
Again, it is a matter of familiar experience to everybody that mere
pressure on the skin will give rise to a corn. Now the gall, the tumour,
and the corn are parts of the living body, which have become, to a
certain degree, independent and distinct organisms. Under the influence
of certain external conditions, elements of the body, which should have
developed in due subordination to its general plan, set up for themselves
and apply the nourishment which they receive to their own purposes.

From such innocent productions as corns and warts, there are all
gradations to the serious tumours which, by their mere size and the
mechanical obstruction they cause, destroy the organism out of which they
are developed; while, finally, in those terrible structures known as
cancers, the abnormal growth has acquired powers of reproduction and
multiplication, and is only morphologically distinguishable from the
parasitic worm, the life of which is neither more nor less closely bound
up with that of the infested organism.

If there were a kind of diseased structure, the histological elements of
which were capable of maintaining a separate and independent existence
out of the body, it seems to me that the shadowy boundary between morbid
growth and Xenogenesis would be effaced. And I am inclined to think that
the progress of discovery has almost brought us to this point already. I
have been favoured by Mr. Simon with an early copy of the last published
of the valuable "Reports on the Public Health," which, in his capacity of
their medical officer, he annually presents to the Lords of the Privy
Council. The appendix to this report contains an introductory essay "On
the Intimate Pathology of Contagion," by Dr. Burdon-Sanderson, which is
one of the clearest, most comprehensive, and well-reasoned discussions of
a great question which has come under my notice for a long time. I refer
you to it for details and for the authorities for the statements I am
about to make.

You are familiar with what happens in vaccination. A minute cut is made
in the skin, and an infinitesimal quantity of vaccine matter is inserted
into the wound. Within a certain time a vesicle appears in the place of
the wound, and the fluid which distends this vesicle is vaccine matter,
in quantity a hundred or a thousandfold that which was originally
inserted. Now what has taken place in the course of this operation? Has
the vaccine matter, by its irritative property, produced a mere blister,
the fluid of which has the same irritative property? Or does the vaccine
matter contain living particles, which have grown and multiplied where
they have been planted? The observations of M. Chauveau, extended and
confirmed by Dr. Sanderson himself, appear to leave no doubt upon this
head. Experiments, similar in principle to those of Helmholtz on
fermentation and putrefaction, have proved that the active element in the
vaccine lymph is non-diffusible, and consists of minute particles not
exceeding 1/20000th of an inch in diameter, which are made visible in the
lymph by the microscope. Similar experiments have proved that two of the
most destructive of epizootic diseases, sheep-pox and glanders, are also
dependent for their existence and their propagation upon extremely small
living solid particles, to which the title of _microzymes_ is applied. An
animal suffering under either of these terrible diseases is a source of
infection and contagion to others, for precisely the same reason as a tub
of fermenting beer is capable of propagating its fermentation by
"infection," or "contagion," to fresh wort. In both cases it is the solid
living particles which are efficient; the liquid in which they float, and
at the expense of which they live, being altogether passive.

Now arises the question, are these microzymes the results of
_Homogenesis_, or of _Xenogenesis?_ are they capable, like the
_Toruloe_ of yeast, of arising only by the development of pre-existing
germs? or may they be, like the constituents of a nut-gall, the results
of a modification and individualisation of the tissues of the body in
which they are found, resulting from the operation of certain conditions?
Are they parasites in the zoological sense, or are they merely what
Virchow has called "heterologous growths"? It is obvious that this
question has the most profound importance, whether we look at it from a
practical or from a theoretical point of view. A parasite may be stamped
out by destroying its germs, but a pathological product can only be
annihilated by removing the conditions which give rise to it.

It appears to me that this great problem will have to be solved for each
zymotic disease separately, for analogy cuts two ways. I have dwelt upon
the analogy of pathological modification, which is in favour of the
xenogenetic origin of microzymes; but I must now speak of the equally
strong analogies in favour of the origin of such pestiferous particles by
the ordinary process of the generation of like from like.

It is, at present, a well-established fact that certain diseases, both of
plants and of animals, which have all the characters of contagious and
infectious epidemics, are caused by minute organisms. The smut of wheat
is a well-known instance of such a disease, and it cannot be doubted that
the grape-disease and the potato-disease fall under the same category.
Among animals, insects are wonderfully liable to the ravages of
contagious and infectious diseases caused by microscopic _Fungi_.

In autumn, it is not uncommon to see flies motionless upon a window-pane,
with a sort of magic circle, in white, drawn round them. On microscopic
examination, the magic circle is found to consist of innumerable spores,
which have been thrown off in all directions by a minute fungus called
_Empusa muscoe_, the spore-forming filaments of which stand out like a
pile of velvet from the body of the fly. These spore-forming filaments
are connected with others which fill the interior of the fly's body like
so much fine wool, having eaten away and destroyed the creature's
viscera. This is the full-grown condition of the _Empusa_. If traced back
to its earliest stages, in flies which are still active, and to all
appearance healthy, it is found to exist in the form of minute corpuscles
which float in the blood of the fly. These multiply and lengthen into
filaments, at the expense of the fly's substance; and when they have at
last killed the patient, they grow out of its body and give off spores.
Healthy flies shut up with diseased ones catch this mortal disease, and
perish like the others. A most competent observer, M. Cohn, who studied
the development of the _Empusa_ very carefully, was utterly unable to
discover in what manner the smallest germs of the _Empusa_ got into the
fly. The spores could not be made to give rise to such germs by
cultivation; nor were such germs discoverable in the air, or in the food
of the fly. It looked exceedingly like a case of Abiogenesis, or, at any
rate, of Xenogenesis; and it is only quite recently that the real course
of events has been made out. It has been ascertained, that when one of
the spores falls upon the body of a fly, it begins to germinate, and
sends out a process which bores its way through the fly's skin; this,
having reached the interior cavities of its body, gives off the minute
floating corpuscles which are the earliest stage of the _Empusa_. The
disease is "contagious," because a healthy fly coming in contact with a
diseased one, from which the spore-bearing filaments protrude, is pretty
sure to carry off a spore or two. It is "infectious" because the spores
become scattered about all sorts of matter in the neighbourhood of the
slain flies.

The silkworm has long been known to be subject to a very fatal and
infectious disease called the _Muscardine_. Audouin transmitted it by
inoculation. This disease is entirely due to the development of a fungus,
_Botrytis Bassiana_, in the body of the caterpillar; and its
contagiousness and infectiousness are accounted for in the same way as
those of the fly-disease. But, of late years, a still more serious
epizootic has appeared among the silkworms; and I may mention a few facts
which will give you some conception of the gravity of the injury which it
has inflicted on France alone.

The production of silk has been for centuries an important branch of
industry in Southern France, and in the year 1853 it had attained such a
magnitude that the annual produce of the French sericulture was estimated
to amount to a tenth of that of the whole world, and represented a money-
value of 117,000,000 francs, or nearly five millions sterling. What may
be the sum which would represent the money-value of all the industries
connected with the working up of the raw silk thus produced, is more than
I can pretend to estimate. Suffice it to say, that the city of Lyons is
built upon French silk as much as Manchester was upon American cotton
before the civil war.

Silkworms are liable to many diseases; and, even before 1853, a peculiar
epizootic, frequently accompanied by the appearance of dark spots upon
the skin (whence the name of "Pebrine" which it has received), had been
noted for its mortality. But in the years following 1853 this malady
broke out with such extreme violence, that, in 1858, the silk-crop was
reduced to a third of the amount which it had reached in 1853; and, up
till within the last year or two, it has never attained half the yield of
1853. This means not only that the great number of people engaged in silk
growing are some thirty millions sterling poorer than they might have
been; it means not only that high prices have had to be paid for imported
silkworm eggs, and that, after investing his money in them, in paying for
mulberry-leaves and for attendance, the cultivator has constantly seen
his silkworms perish and himself plunged in ruin; but it means that the
looms of Lyons have lacked employment, and that, for years, enforced
idleness and misery have been the portion of a vast population which, in
former days, was industrious and well-to-do.

In 1858 the gravity of the situation caused the French Academy of
Sciences to appoint Commissioners, of whom a distinguished naturalist, M.
de Quatrefages, was one, to inquire into the nature of this disease, and,
if possible, to devise some means of staying the plague. In reading the
Report[11] made by M. de Quatrefages in 1859, it is exceedingly
interesting to observe that his elaborate study of the Pebrine forced the
conviction upon his mind that, in its mode of occurrence and propagation,
the disease of the silkworm is, in every respect, comparable to the
cholera among mankind. But it differs from the cholera, and so far is a
more formidable malady, in being hereditary, and in being, under some
circumstances, contagious as well as infectious.

[Footnote 11: _Etudes sur les Maladies actuelles des Vers a Soie_, p.
53.]

The Italian naturalist, Filippi, discovered in the blood of the silkworms
affected by this strange disorder a multitude of cylindrical corpuscles,
each about 1/6000th of an inch long. These have been carefully studied by
Lebert, and named by him _Panhistophyton_; for the reason that in
subjects in which the disease is strongly developed, the corpuscles swarm
in every tissue and organ of the body, and even pass into the undeveloped
eggs of the female moth. But are these corpuscles causes, or mere
concomitants, of the disease? Some naturalists took one view and some
another; and it was not until the French Government, alarmed by the
continued ravages of the malady, and the inefficiency of the remedies
which had been suggested, despatched M. Pasteur to study it, that the
question received its final settlement; at a great sacrifice, not only of
the time and peace of mind of that eminent philosopher, but, I regret to
have to add, of his health.

But the sacrifice has not been in vain. It is now certain that this
devastating, cholera-like, Pebrine, is the effect of the growth and
multiplication of the _Panhistophyton_ in the silkworm. It is contagious
and infectious, because the corpuscles of the _Panhistophyton_ pass away
from the bodies of the diseased caterpillars, directly or indirectly, to
the alimentary canal of healthy silkworms in their neighbourhood; it is
hereditary because the corpuscles enter into the eggs while they are
being formed, and consequently are carried within them when they are
laid; and for this reason, also, it presents the very singular
peculiarity of being inherited only on the mother's side. There is not a
single one of all the apparently capricious and unaccountable phenomena
presented by the Pebrine, but has received its explanation from the fact
that the disease is the result of the presence of the microscopic
organism, _Panhistophyton_.

Such being the facts with respect to the Pebrine, what are the
indications as to the method of preventing it? It is obvious that this
depends upon the way in which the _Panhistophyton_ is generated. If it
may be generated by Abiogenesis, or by Xenogenesis, within the silkworm
or its moth, the extirpation of the disease must depend upon the
prevention of the occurrence of the conditions under which this
generation takes place. But if, on the other hand, the _Panhistophyton_
is an independent organism, which is no more generated by the silkworm
than the mistletoe is generated by the apple-tree or the oak on which it
grows, though it may need the silkworm for its development in the same
way as the mistletoe needs the tree, then the indications are totally
different. The sole thing to be done is to get rid of and keep away the
germs of the _Panhistophyton_. As might be imagined, from the course of
his previous investigations, M. Pasteur was led to believe that the
latter was the right theory; and, guided by that theory, he has devised a
method of extirpating the disease, which has proved to be completely
successful wherever it has been properly carried out.

There can be no reason, then, for doubting that, among insects,
contagious and infectious diseases, of great malignity, are caused by
minute organisms which are produced from pre-existing germs, or by
homogenesis; and there is no reason, that I know of, for believing that
what happens in insects may not take place in the highest animals.
Indeed, there is already strong evidence that some diseases of an
extremely malignant and fatal character to which man is subject, are as
much the work of minute organisms as is the Pebrine. I refer for this
evidence to the very striking facts adduced by Professor Lister in his
various well-known publications on the antiseptic method of treatment. It
appears to me impossible to rise from the perusal of those publications
without a strong conviction that the lamentable mortality which so
frequently dogs the footsteps of the most skilful operator, and those
deadly consequences of wounds and injuries which seem to haunt the very
walls of great hospitals, and are, even now, destroying more men than die
of bullet or bayonet, are due to the importation of minute organisms into
wounds, and their increase and multiplication; and that the surgeon who
saves most lives will be he who best works out the practical consequences
of the hypothesis of Redi.

I commenced this Address by asking you to follow me in an attempt to
trace the path which has been followed by a scientific idea, in its long
and slow progress from the position of a probable hypothesis to that of
an established law of nature. Our survey has not taken us into very
attractive regions; it has lain, chiefly, in a land flowing with the
abominable, and peopled with mere grubs and mouldiness. And it may be
imagined with what smiles and shrugs, practical and serious
contemporaries of Redi and of Spallanzani may have commented on the waste
of their high abilities in toiling at the solution of problems which,
though curious enough in themselves, could be of no conceivable utility
to mankind.

Nevertheless, you will have observed that before we had travelled very
far upon our road, there appeared, on the right hand and on the left,
fields laden with a harvest of golden grain, immediately convertible into
those things which the most solidly practical men will admit to have
value--viz., money and life.

The direct loss to France caused by the Pebrine in seventeen years cannot
be estimated at less than fifty millions sterling; and if we add to this
what Redi's idea, in Pasteur's hands, has done for the wine-grower and
for the vinegar-maker, and try to capitalise its value, we shall find
that it will go a long way towards repairing the money losses caused by
the frightful and calamitous war of this autumn. And as to the equivalent
of Redi's thought in life, how can we over-estimate the value of that
knowledge of the nature of epidemic and epizootic diseases, and
consequently of the means of checking, or eradicating them, the dawn of
which has assuredly commenced?

Looking back no further than ten years, it is possible to select three
(1863, 1864, and 1869) in which the total number of deaths from scarlet-
fever alone amounted to ninety thousand. That is the return of killed,
the maimed and disabled being left out of sight. Why, it is to be hoped
that the list of killed in the present bloodiest of all wars will not
amount to more than this! But the facts which I have placed before you
must leave the least sanguine without a doubt that the nature and the
causes of this scourge will, one day, be as well understood as those of
the Pebrine are now; and that the long-suffered massacre of our innocents
will come to an end.

And thus mankind will have one more admonition that "the people perish
for lack of knowledge"; and that the alleviation of the miseries, and the
promotion of the welfare, of men must be sought, by those who will not
lose their pains, in that diligent, patient, loving study of all the
multitudinous aspects of Nature, the results of which constitute exact
knowledge, or Science. It is the justification and the glory of this
great meeting that it is gathered together for no other object than the
advancement of the moiety of science which deals with those phenomena of
nature which we call physical. May its endeavours be crowned with a full
measure of success!



IX


GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE

[1862]

Merchants occasionally go through a wholesome, though troublesome and not
always satisfactory, process which they term "taking stock." After all
the excitement of speculation, the pleasure of gain, and the pain of
loss, the trader makes up his mind to face facts and to learn the exact
quantity and quality of his solid and reliable possessions.

The man of science does well sometimes to imitate this procedure; and,
forgetting for the time the importance of his own small winnings, to re-
examine the common stock in trade, so that he may make sure how far the
stock of bullion in the cellar--on the faith of whose existence so much
paper has been circulating--is really the solid gold of truth.

The Anniversary Meeting of the Geological Society seems to be an occasion
well suited for an undertaking of this kind--for an inquiry, in fact,
into the nature and value of the present results of palaeontological
investigation; and the more so, as all those who have paid close
attention to the late multitudinous discussions in which palaeontology is
implicated, must have felt the urgent necessity of some such scrutiny.

First in order, as the most definite and unquestionable of all the
results of palaeontology, must be mentioned the immense extension and
impulse given to botany, zoology, and comparative anatomy, by the
investigation of fossil remains. Indeed, the mass of biological facts has
been so greatly increased, and the range of biological speculation has
been so vastly widened, by the researches of the geologist and
palaeontologist, that it is to be feared there are naturalists in
existence who look upon geology as Brindley regarded rivers. "Rivers,"
said the great engineer, "were made to feed canals;" and geology, some
seem to think, was solely created to advance comparative anatomy.

Were such a thought justifiable, it could hardly expect to be received
with favour by this assembly. But it is not justifiable. Your favourite
science has her own great aims independent of all others; and if,
notwithstanding her steady devotion to her own progress, she can scatter
such rich alms among her sisters, it should be remembered that her
charity is of the sort that does not impoverish, but "blesseth him that
gives and him that takes."

Regard the matter as we will, however, the facts remain. Nearly 40,000
species of animals and plants have been added to the Systema Naturae by
palaeontological research. This is a living population equivalent to that
of a new continent in mere number; equivalent to that of a new
hemisphere, if we take into account the small population of insects as
yet found fossil, and the large proportion and peculiar organisation of
many of the Vertebrata.

But, beyond this, it is perhaps not too much to say that, except for the
necessity of interpreting palaeontological facts, the laws of distribution
would have received less careful study; while few comparative anatomists
(and those not of the first order) would have been induced by mere love
of detail, as such, to study the minutiae of osteology, were it not that
in such minutiae lie the only keys to the most interesting riddles offered
by the extinct animal world.

These assuredly are great and solid gains. Surely it is matter for no
small congratulation that in half a century (for palaeontology, though it
dawned earlier, came into full day only with Cuvier) a subordinate branch
of biology should have doubled the value and the interest of the whole
group of sciences to which it belongs.

But this is not all. Allied with geology, palaeontology has established
two laws of inestimable importance: the first, that one and the same area
of the earth's surface has been successively occupied by very different
kinds of living beings; the second, that the order of succession
established in one locality holds good, approximately, in all.

The first of these laws is universal and irreversible; the second is an
induction from a vast number of observations, though it may possibly, and
even probably, have to admit of exceptions. As a consequence of the
second law, it follows that a peculiar relation frequently subsists
between series of strata containing organic remains, in different
localities. The series resemble one another not only in virtue of a
general resemblance of the organic remains in the two, but also in virtue
of a resemblance in the order and character of the serial succession in
each. There is a resemblance of arrangement; so that the separate terms
of each series, as well as the whole series, exhibit a correspondence.

Succession implies time; the lower members of an undisturbed series of
sedimentary rocks are certainly older than the upper; and when the notion
of age was once introduced as the equivalent of succession, it was no
wonder that correspondence in succession came to be looked upon as a
correspondence in age, or "contemporaneity." And, indeed, so long as
relative age only is spoken of, correspondence in succession _is_
correspondence in age; it is _relative_ contemporaneity.

But it would have been very much better for geology if so loose and
ambiguous a word as "contemporaneous" had been excluded from her
terminology, and if, in its stead, some term expressing similarity of
serial relation, and excluding the notion of time altogether, had been
employed to denote correspondence in position in two or more series of
strata.

In anatomy, where such correspondence of position has constantly to be
spoken of, it is denoted by the word "homology" and its derivatives; and
for Geology (which after all is only the anatomy and physiology of the
earth) it might be well to invent some single word, such as "homotaxis"
(similarity of order), in order to express an essentially similar idea.
This, however, has not been done, and most probably the inquiry will at
once be made--To what end burden science with a new and strange term in
place of one old, familiar, and part of our common language?

The reply to this question will become obvious as the inquiry into the
results of palaeontology is pushed further.

Those whose business it is to acquaint themselves specially with the
works of palaeontologists, in fact, will be fully aware that very few, if
any, would rest satisfied with such a statement of the conclusions of
their branch of biology as that which has just been given.

Our standard repertories of palaeontology profess to teach us far higher
things--to disclose the entire succession of living forms upon the
surface of the globe; to tell us of a wholly different distribution of
climatic conditions in ancient times; to reveal the character of the
first of all living existences; and to trace out the law of progress from
them to us.

It may not be unprofitable to bestow on these professions a somewhat more
critical examination than they have hitherto received, in order to
ascertain how far they rest on an irrefragable basis; or whether, after
all, it might not be well for palaeontologists to learn a little more
carefully that scientific "ars artium," the art of saying "I don't know."
And to this end let us define somewhat more exactly the extent of these
pretensions of palaeontology.

Every one is aware that Professor Bronn's "Untersuchungen" and Professor
Pictet's "Traite de Paleontologie" are works of standard authority,
familiarly consulted by every working palaeontologist. It is desirable to
speak of these excellent books, and of their distinguished authors, with
the utmost respect, and in a tone as far as possible removed from carping
criticism; indeed, if they are specially cited in this place, it is
merely in justification of the assertion that the following propositions,
which may be found implicitly, or explicitly, in the works in question,
are regarded by the mass of palaeontologists and geologists, not only on
the Continent but in this country, as expressing some of the best-
established results of palaeontology. Thus:--

Animals and plants began their existence together, not long after the
commencement of the deposition of the sedimentary rocks; and then
succeeded one another, in such a manner, that totally distinct faunae and
florae occupied the whole surface of the earth, one after the other, and
during distinct epochs of time.

A geological formation is the sum of all the strata deposited over the
whole surface of the earth during one of these epochs: a geological fauna
or flora is the sum of all the species of animals or plants which
occupied the whole surface of the globe, during one of these epochs.

The population of the earth's surface was at first very similar in all
parts, and only from the middle of the Tertiary epoch onwards, began to
show a distinct distribution in zones.

The constitution of the original population, as well as the numerical
proportions of its members, indicates a warmer and, on the whole,
somewhat tropical climate, which remained tolerably equable throughout
the year. The subsequent distribution of living beings in zones is the
result of a gradual lowering of the general temperature, which first
began to be felt at the poles.

It is not now proposed to inquire whether these doctrines are true or
false; but to direct your attention to a much simpler though very
essential preliminary question--What is their logical basis? what are the
fundamental assumptions upon which they all logically depend? and what is
the evidence on which those fundamental propositions demand our assent?

These assumptions are two: the first, that the commencement of the
geological record is coeval with the commencement of life on the globe;
the second, that geological contemporaneity is the same thing as
chronological synchrony. Without the first of these assumptions there
would of course be no ground for any statement respecting the
commencement of life; without the second, all the other statements cited,
every one of which implies a knowledge of the state of different parts of
the earth at one and the same time, will be no less devoid of
demonstration.

The first assumption obviously rests entirely on negative evidence. This
is, of course, the only evidence that ever can be available to prove the
commencement of any series of phenomena; but, at the same time, it must
be recollected that the value of negative evidence depends entirely on
the amount of positive corroboration it receives. If A.B. wishes to prove
an _alibi_, it is of no use for him to get a thousand witnesses simply to
swear that they did not see him in such and such a place, unless the
witnesses are prepared to prove that they must have seen him had he been
there. But the evidence that animal life commenced with the Lingula-
flags, _e.g._, would seem to be exactly of this unsatisfactory
uncorroborated sort. The Cambrian witnesses simply swear they "haven't
seen anybody their way"; upon which the counsel for the other side
immediately puts in ten or twelve thousand feet of Devonian sandstones to
make oath they never saw a fish or a mollusk, though all the world knows
there were plenty in their time.

But then it is urged that, though the Devonian rocks in one part of the
world exhibit no fossils, in another they do, while the lower Cambrian
rocks nowhere exhibit fossils, and hence no living being could have
existed in their epoch.

To this there are two replies: the first that the observational basis of
the assertion that the lowest rocks are nowhere fossiliferous is an
amazingly small one, seeing how very small an area, in comparison to that
of the whole world, has yet been fully searched; the second, that the
argument is good for nothing unless the unfossiliferous rocks in question
were not only _contemporaneous_ in the geological sense, but
_synchronous_ in the chronological sense. To use the _alibi_ illustration
again. If a man wishes to prove he was in neither of two places, A and B,
on a given day, his witnesses for each place must be prepared to answer
for the whole day. If they can only prove that he was not at A in the
morning, and not at B in the afternoon, the evidence of his absence from
both is nil, because he might have been at B in the morning and at A in
the afternoon.

Thus everything depends upon the validity of the second assumption. And
we must proceed to inquire what is the real meaning of the word
"contemporaneous" as employed by geologists. To this end a concrete
example may be taken.

The Lias of England and the Lias of Germany, the Cretaceous rocks of
Britain and the Cretaceous rocks of Southern India, are termed by
geologists "contemporaneous" formations; but whenever any thoughtful
geologist is asked whether he means to say that they were deposited
synchronously, he says, "No,--only within the same great epoch." And if,
in pursuing the inquiry, he is asked what may be the approximate value in
time of a "great epoch"--whether it means a hundred years, or a thousand,
or a million, or ten million years--his reply is, "I cannot tell."

If the further question be put, whether physical geology is in possession
of any method by which the actual synchrony (or the reverse) of any two
distant deposits can be ascertained, no such method can be heard of; it
being admitted by all the best authorities that neither similarity of
mineral composition, nor of physical character, nor even direct
continuity of stratum, are _absolute_ proofs of the synchronism of even
approximated sedimentary strata: while, for distant deposits, there seems
to be no kind of physical evidence attainable of a nature competent to
decide whether such deposits were formed simultaneously, or whether they
possess any given difference of antiquity. To return to an example
already given: All competent authorities will probably assent to the
proposition that physical geology does not enable us in any way to reply
to this question--Were the British Cretaceous rocks deposited at the same
time as those of India, or are they a million of years younger or a
million of years older?

Is palaeontology able to succeed where physical geology fails? Standard
writers on palaeontology, as has been seen, assume that she can. They take
it for granted, that deposits containing similar organic remains are
synchronous--at any rate in a broad sense; and yet, those who will study
the eleventh and twelfth chapters of Sir Henry De La Beche's remarkable
"Researches in Theoretical Geology," published now nearly thirty years
ago, and will carry out the arguments there most luminously stated, to
their logical consequences, may very easily convince themselves that even
absolute identity of organic contents is no proof of the synchrony of
deposits, while absolute diversity is no proof of difference of date. Sir
Henry De La Beche goes even further, and adduces conclusive evidence to
show that the different parts of one and the same stratum, having a
similar composition throughout, containing the same organic remains, and
having similar beds above and below it, may yet differ to any conceivable
extent in age.

Edward Forbes was in the habit of asserting that the similarity of the
organic contents of distant formations was _prima facie_ evidence, not of
their similarity, but of their difference of age; and holding as he did
the doctrine of single specific centres, the conclusion was as legitimate
as any other; for the two districts must have been occupied by migration
from one of the two, or from an intermediate spot, and the chances
against exact coincidence of migration and of imbedding are infinite.

In point of fact, however, whether the hypothesis of single or of
multiple specific centres be adopted, similarity of organic contents
cannot possibly afford any proof of the synchrony of the deposits which
contain them; on the contrary, it is demonstrably compatible with the
lapse of the most prodigious intervals of time, and with the
interposition of vast changes in the organic and inorganic worlds,
between the epochs in which such deposits were formed.

On what amount of similarity of their faunae is the doctrine of the
contemporaneity of the European and of the North American Silurians
based? In the last edition of Sir Charles Lyell's "Elementary Geology" it
is stated, on the authority of a former President of this Society, the
late Daniel Sharpe, that between 30 and 40 per cent. of the species of
Silurian Mollusca are common to both sides of the Atlantic. By way of due
allowance for further discovery, let us double the lesser number and
suppose that 60 per cent. of the species are common to the North American
and the British Silurians. Sixty per cent. of species in common is, then,
proof of contemporaneity.

Now suppose that, a million or two of years hence, when Britain has made
another dip beneath the sea and has come up again, some geologist applies
this doctrine, in comparing the strata laid bare by the upheaval of the
bottom, say, of St. George's Channel with what may then remain of the
Suffolk Crag. Reasoning in the same way, he will at once decide the
Suffolk Crag and the St. George's Channel beds to be contemporaneous;
although we happen to know that a vast period (even in the geological
sense) of time, and physical changes of almost unprecedented extent,
separate the two. But if it be a demonstrable fact that strata
containing more than 60 or 70 per cent. of species of Mollusca in common,
and comparatively close together, may yet be separated by an amount of
geological time sufficient to allow of some of the greatest physical
changes the world has seen, what becomes of that sort of contemporaneity
the sole evidence of which is a similarity of facies, or the identity of
half a dozen species, or of a good many genera?

And yet there is no better evidence for the contemporaneity assumed by
all who adopt the hypothesis of universal faunae and florae, of a
universally uniform climate, and of a sensible cooling of the globe
during geological time.

There seems, then, no escape from the admission that neither physical
geology, nor palaeontology, possesses any method by which the absolute
synchronism of two strata can be demonstrated. All that geology can prove
is local order of succession. It is mathematically certain that, in any
given vertical linear section of an undisturbed series of sedimentary
deposits, the bed which lies lowest is the oldest. In many other vertical
linear sections of the same series, of course, corresponding beds will
occur in a similar order; but, however great may be the probability, no
man can say with absolute certainty that the beds in the two sections
were synchronously deposited. For areas of moderate extent, it is
doubtless true that no practical evil is likely to result from assuming
the corresponding beds to be synchronous or strictly contemporaneous; and
there are multitudes of accessory circumstances which may fully justify
the assumption of such synchrony. But the moment the geologist has to
deal with large areas, or with completely separated deposits, the
mischief of confounding that "homotaxis" or "similarity of arrangement,"
which _can_ be demonstrated, with "synchrony" or "identity of date," for
which there is not a shadow of proof, under the one common term of
"contemporaneity" becomes incalculable, and proves the constant source of
gratuitous speculations.

For anything that geology or palaeontology are able to show to the
contrary, a Devonian fauna and flora in the British Islands may have been
contemporaneous with Silurian life in North America, and with a
Carboniferous fauna and flora in Africa. Geographical provinces and zones
may have been as distinctly marked in the Palaeozoic epoch as at present,
and those seemingly sudden appearances of new genera and species, which
we ascribe to new creation, may be simple results of migration.

It may be so; it may be otherwise. In the present condition of our
knowledge and of our methods, one verdict--"not proven, and not
provable"--must be recorded against all the grand hypotheses of the
palaeontologist respecting the general succession of life on the globe.
The order and nature of terrestrial life, as a whole, are open questions.
Geology at present provides us with most valuable topographical records,
but she has not the means of working them into a universal history. Is
such a universal history, then, to be regarded as unattainable? Are all
the grandest and most interesting problems which offer themselves to the
geological student, essentially insoluble? Is he in the position of a
scientific Tantalus--doomed always to thirst for a knowledge which he
cannot obtain? The reverse is to be hoped; nay, it may not be impossible
to indicate the source whence help will come.

In commencing these remarks, mention was made of the great obligations
under which the naturalist lies to the geologist and palaeontologist.
Assuredly the time will come when these obligations will be repaid
tenfold, and when the maze of the world's past history, through which the
pure geologist and the pure palaeontologist find no guidance, will be
securely threaded by the clue furnished by the naturalist.

All who are competent to express an opinion on the subject are, at
present, agreed that the manifold varieties of animal and vegetable form
have not either come into existence by chance, nor result from capricious
exertions of creative power; but that they have taken place in a definite
order, the statement of which order is what men of science term a natural
law. Whether such a law is to be regarded as an expression of the mode of
operation of natural forces, or whether it is simply a statement of the
manner in which a supernatural power has thought fit to act, is a
secondary question, so long as the existence of the law and the
possibility of its discovery by the human intellect are granted. But he
must be a half-hearted philosopher who, believing in that possibility,
and having watched the gigantic strides of the biological sciences during
the last twenty years, doubts that science will sooner or later make this
further step, so as to become possessed of the law of evolution of
organic forms--of the unvarying order of that great chain of causes and
effects of which all organic forms, ancient and modern, are the links.
And then, if ever, we shall be able to begin to discuss, with profit, the
questions respecting the commencement of life, and the nature of the
successive populations of the globe, which so many seem to think are
already answered.

The preceding arguments make no particular claim to novelty; indeed they
have been floating more or less distinctly before the minds of geologists
for the last thirty years; and if, at the present time, it has seemed
desirable to give them more definite and systematic expression, it is
because palaeontology is every day assuming a greater importance, and now
requires to rest on a basis the firmness of which is thoroughly well
assured. Among its fundamental conceptions, there must be no confusion
between what is certain and what is more or less probable.[1] But,
pending the construction of a surer foundation than palaeontology now
possesses, it may be instructive, assuming for the nonce the general
correctness of the ordinary hypothesis of geological contemporaneity, to
consider whether the deductions which are ordinarily drawn from the whole
body of palaeontological facts are justifiable.

[Footnote 1: "Le plus grand service qu'on puisse rendre a la science est
d'y faire place nette avant d'y rien construire."--CUVIER.]

The evidence on which such conclusions are based is of two kinds,
negative and positive. The value of negative evidence, in connection with
this inquiry, has been so fully and clearly discussed in an address from
the chair of this Society,[2] which none of us have forgotten, that
nothing need at present be said about it; the more, as the considerations
which have been laid before you have certainly not tended to increase
your estimation of such evidence. It will be preferable to turn to the
positive facts of palaeontology, and to inquire what they tell us.

[Footnote 2: Anniversary Address for 1851, _Quart. Journ. Geol. Soc._
vol. vii.]

We are all accustomed to speak of the number and the extent of the
changes in the living population of the globe during geological time as
something enormous: and indeed they are so, if we regard only the
negative differences which separate the older rocks from the more modern,
and if we look upon specific and generic changes as great changes, which
from one point of view, they truly are. But leaving the negative
differences out of consideration, and looking only at the positive data
furnished by the fossil world from a broader point of view--from that of
the comparative anatomist who has made the study of the greater
modifications of animal form his chief business--a surprise of another
kind dawns upon the mind; and under _this_ aspect the smallness of the
total change becomes as astonishing as was its greatness under the other.

There are two hundred known orders of plants; of these not one is
certainly known to exist exclusively in the fossil state. The whole lapse
of geological time has as yet yielded not a single new ordinal type of
vegetable structure.[3]

[Footnote 3: See Hooker's _Introductory Essay to the Flora of Tasmania_,
p. xxiii.]

The positive change in passing from the recent to the ancient animal
world is greater, but still singularly small. No fossil animal is so
distinct from those now living as to require to be arranged even in a
separate class from those which contain existing forms. It is only when
we come to the orders, which may be roughly estimated at about a hundred
and thirty, that we meet with fossil animals so distinct from those now
living as to require orders for themselves; and these do not amount, on
the most liberal estimate, to more than about 10 per cent. of the whole.

There is no certainly known extinct order of Protozoa; there is but one
among the Coelenterata--that of the rugose corals; there is none among
the Mollusca; there are three, the Cystidea, Blastoidea, and
Edrioasterida, among the Echinoderms; and two, the Trilobita and
Eurypterida, among the Crustacea; making altogether five for the great
sub-kingdom of Annulosa. Among Vertebrates there is no ordinally distinct
fossil fish: there is only one extinct order of Amphibia--the
Labyrinthodonts; but there are at least four distinct orders of Reptilia,
viz. the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, and
perhaps another or two. There is no known extinct order of Birds, and no
certainly known extinct order of Mammals, the ordinal distinctness of the
"Toxodontia" being doubtful.

The objection that broad statements of this kind, after all, rest largely
on negative evidence is obvious, but it has less force than may at first
be supposed; for, as might be expected from the circumstances of the
case, we possess more abundant positive evidence regarding Fishes and
marine Mollusks than respecting any other forms of animal life; and yet
these offer us, through the whole range of geological time, no species
ordinally distinct from those now living; while the far less numerous
class of Echinoderms presents three, and the Crustacea two, such orders,
though none of these come down later than the Palaeozoic age. Lastly, the
Reptilia present the extraordinary and exceptional phenomenon of as many
extinct as existing orders, if not more; the four mentioned maintaining
their existence from the Lias to the Chalk inclusive.

Some years ago one of your Secretaries pointed out another kind of
positive palaeontological evidence tending towards the same conclusion--
afforded by the existence of what he termed "persistent types" of
vegetable and of animal life.[4] He stated, on the authority of Dr.
Hooker, that there are Carboniferous plants which appear to be
generically identical with some now living; that the cone of the Oolitic
_Araucaria_ is hardly distinguishable from that of an existing species;
that a true _Pinus_ appears in the Purbecks and a _Juglans_ in the Chalk;
while, from the Bagshot Sands, a _Banksia_, the wood of which is not
distinguishable from that of species now living in Australia, had been
obtained.

[Footnote 4: See the abstract of a Lecture "On the Persistent Types of
Animal Life," in the _Notices of the Meetings of the Royal Institution of
Great Britain_.--June 3, 1859, vol. iii. p. 151.]

Turning to the animal kingdom, he affirmed the tabulate corals of the
Silurian rocks to be wonderfully like those which now exist; while even
the families of the Aporosa were all represented in the older Mesozoic
rocks.

Among the Mollusca similar facts were adduced. Let it be borne in mind
that _Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina,
Orbicula, Lingula, Rhynchonclla_, and _Nautilus_, all of which are
existing _genera_, are given without a doubt as Silurian in the last
edition of "Siluria"; while the highest forms of the highest Cephalopods
are represented in the Lias by a genus _Belemnoteuthis_, which presents
the closest relation to the existing _Loligo_.

The two highest groups of the Annulosa, the Insecta and the Arachnida,
are represented in the Coal, either by existing genera, or by forms
differing from existing genera in quite minor peculiarities.

Turning to the Vertebrata, the only palaeozoic Elasmobranch Fish of which
we have any complete knowledge is the Devonian and Carboniferous
_Pleuracanthus_, which differs no more from existing Sharks than these do
from one another.

Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and
great as is their range in time, a large mass of evidence has recently
been adduced to show that almost all those respecting which we possess
sufficient information, are referable to the same sub-ordinal groups as
the existing _Lepidosteus, Polypterus_, and Sturgeon; and that a singular
relation obtains between the older and the younger Fishes; the former,
the Devonian Ganoids, being almost all members of the same sub-order as
_Polypterus_, while the Mesozoic Ganoids are almost all similarly allied
to _Lepidosteus_.[5]

[Footnote 5: "Memoirs of the Geological Survey of the United Kingdom.--
Decade x. Preliminary Essay upon the Systematic Arrangement of the Fishes
of the Devonian Epoch."]

Again, what can be more remarkable than the singular constancy of
structure preserved throughout a vast period of time by the family of the
Pycnodonts and by that of the true Coelacanths; the former persisting,
with but insignificant modifications, from the Carboniferous to the
Tertiary rocks, inclusive; the latter existing, with still less change,
from the Carboniferous rocks to the Chalk, inclusive?

Among Reptiles, the highest living group, that of the Crocodilia, is
represented, at the early part of the Mesozoic epoch, by species
identical in the essential characters of their organisation with those
now living, and differing from the latter only in such matters as the
form of the articular facets of the vertebral centra, in the extent to
which the nasal passages are separated from the cavity of the mouth by
bone, and in the proportions of the limbs.

And even as regards the Mammalia, the scanty remains of Triassic and
Oolitic species afford no foundation for the supposition that the
organisation of the oldest forms differed nearly so much from some of
those which now live as these differ from one another.

It is needless to multiply these instances; enough has been said to
justify the statement that, in view of the immense diversity of known
animal and vegetable forms, and the enormous lapse of time indicated by
the accumulation of fossiliferous strata, the only circumstance to be
wondered at is, not that the changes of life, as exhibited by positive
evidence, have been so great but that they have been so small.

Be they great or small, however, it is desirable to attempt to estimate
them. Let us, therefore, take each great division of the animal world in
succession, and, whenever an order or a family can be shown to have had a
prolonged existence, let us endeavour to ascertain how far the later
members of the group differ from the earlier ones. If these later
members, in all or in many cases, exhibit a certain amount of
modification, the fact is, so far, evidence in favour of a general law of
change; and, in a rough way, the rapidity of that change will be measured
by the demonstrable amount of modification. On the other hand, it must be
recollected that the absence of any modification, while it may leave the
doctrine of the existence of a law of change without positive support,
cannot possibly disprove all forms of that doctrine, though it may afford
a sufficient refutation of many of them.

The PROTOZOA.--The Protozoa are represented throughout the whole range of
geological series, from the Lower Silurian formation to the present day.
The most ancient forms recently made known by Ehrenberg are exceedingly
like those which now exist: no one has ever pretended that the difference
between any ancient and any modern Foraminifera is of more than generic
value, nor are the oldest Foraminifera either simpler, more embryonic, or
less differentiated, than the existing forms.

The COELENTERATA.--The Tabulate Corals have existed from the Silurian
epoch to the present day, but I am not aware that the ancient
_Heliolites_ possesses a single mark of a more embryonic or less
differentiated character, or less high organisation, than the existing
_Heliopora_. As for the Aporose Corals, in what respect is the Silurian
_Paloeocyclus_ less highly organised or more embryonic than the modern
_Fungia_, or the Liassic Aporosa than the existing members of the same
families?

The _Mollusca_--In what sense is the living _Waldheimia_ less embryonic,
or more specialised, than the palaeozoic _Spirifer_; or the existing
_Rhynchonelloe, Cranioe, Discinoe, Linguloe_, than the Silurian species
of the same genera? In what sense can _Loligo_ or _Spirula_ be said to be
more specialised, or less embryonic, than _Belemnites_; or the modern
species of Lamellibranch and Gasteropod genera, than the Silurian species
of the same genera?

The ANNULOSA.--The Carboniferous Insecta and Arachnida are neither less
specialised, nor more embryonic, than these that now live, nor are the
Liassic Cirripedia and Macrura; while several of the Brachyura, which
appear in the Chalk, belong to existing genera; and none exhibit either
an intermediate, or an embryonic, character.

The VERTEBRATA.--Among fishes I have referred to the Coelacanthini
(comprising the genera _Coelacanthus, Holophagus, Undina_, and
_Macropoma_) as affording an example of a persistent type; and it is most
remarkable to note the smallness of the differences between any of these
fishes (affecting at most the proportions of the body and fins, and the
character and sculpture of the scales), notwithstanding their enormous
range in time. In all the essentials of its very peculiar structure, the
_Macropoma_ of the Chalk is identical with the _Coelacanthus_ of the
Coal. Look at the genus _Lepidotus_, again, persisting without a
modification of importance from the Liassic to the Eocene formations
inclusively.

Or among the Teleostei--in what respect is the _Beryx_ of the Chalk more
embryonic, or less differentiated, than _Beryx lineatus_ of King George's
Sound?

Or to turn to the higher Vertebrata--in what sense are the Liassic
Chelonia inferior to those which now exist? How are the Cretaceous
Ichthyosauria, Plesiosauria, or Pterosauria less embryonic, or more
differentiated, species than those of the Lias?

Or lastly, in what circumstance is the _Phascolotherium_ more embryonic,
or of a more generalised type, than the modern Opossum; or a _Lophiodon_,
or a _Paloeotherium_, than a modern _Tapirus_ or _Hyrax_?

These examples might be almost indefinitely multiplied, but surely they
are sufficient to prove that the only safe and unquestionable testimony
we can procure--positive evidence--fails to demonstrate any sort of
progressive modification towards a less embryonic, or less generalised,
type in a great many groups of animals of long-continued geological
existence. In these groups there is abundant evidence of variation--none
of what is ordinarily understood as progression; and, if the known
geological record is to be regarded as even any considerable fragment of
the whole, it is inconceivable that any theory of a necessarily
progressive development can stand, for the numerous orders and families
cited afford no trace of such a process.

But it is a most remarkable fact, that, while the groups which have been
mentioned, and many besides, exhibit no sign of progressive modification,
there are others, co-existing with them, under the same conditions, in
which more or less distinct indications of such a process seems to be
traceable. Among such indications I may remind you of the predominance of
Holostome Gasteropoda in the older rocks as compared with that of
Siphonostone Gasteropoda in the later. A case less open to the objection
of negative evidence, however, is that afforded by the Tetrabranchiate
Cephalopoda, the forms of the shells and of the septal sutures exhibiting
a certain increase of complexity in the newer genera. Here, however, one
is met at once with the occurrence of _Orthoceras_ and _Baculites_ at the
two ends of the series, and of the fact that one of the simplest genera,
_Nautilus_, is that which now exists.

The Crinoidea, in the abundance of stalked forms in the ancient
formations as compared with their present rarity, seem to present us with
a fair case of modification from a more embryonic towards a less
embryonic condition. But then, on careful consideration of the facts, the
objection arises that the stalk, calyx, and arms of the palaeozoic Crinoid
are exceedingly different from the corresponding organs of a larval
_Comatula_; and it might with perfect justice be argued that
_Actinocrinus_ and _Eucalyptocrinus_, for example, depart to the full as
widely, in one direction, from the stalked embryo of _Comatula_, as
_Comatula_ itself does in the other.

The Echinidea, again, are frequently quoted as exhibiting a gradual
passage from a more generalised to a more specialised type, seeing that
the elongated, or oval, Spatangoids appear after the spheroidal
Echinoids. But here it might be argued, on the other hand, that the
spheroidal Echinoids, in reality, depart further from the general plan
and from the embryonic form than the elongated Spatangoids do; and that
the peculiar dental apparatus and the pedicellariae of the former are
marks of at least as great differentiation as the petaloid ambulacra and
semitae of the latter.

Once more, the prevalence of Macrurous before Brachyurous Podophthalmia
is, apparently, a fair piece of evidence in favour of progressive
modification in the same order of Crustacea; and yet the case will not
stand much sifting, seeing that the Macrurous Podophthalmia depart as far
in one direction from the common type of Podophthalmia, or from any
embryonic condition of the Brachyura, as the Brachyura do in the other;
and that the middle terms between Macrura and Brachyura--the Anomura--are
little better represented in the older Mesozoic rocks than the Brachyura
are.

None of the cases of progressive modification which are cited from among
the Invertebrata appear to me to have a foundation less open to criticism
than these; and if this be so, no careful reasoner would, I think, be
inclined to lay very great stress upon them. Among the Vertebrata,
however, there are a few examples which appear to be far less open to
objection.

It is, in fact, true of several groups of Vertebrata which have lived
through a considerable range of time, that the endoskeleton (more
particularly the spinal column) of the older genera presents a less
ossified, and, so far, less differentiated, condition than that of the
younger genera. Thus the Devonian Ganoids, though almost all members of
the same sub-order as _Polypterus_, and presenting numerous important
resemblances to the existing genus, which possesses biconclave vertebrae,
are, for the most part, wholly devoid of ossified vertebral centra. The
Mesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, while
the existing _Lepidosteus_ has Salamandroid, opisthocoelous, vertebrae.
So, none of the Palaeozoic Sharks have shown themselves to be possessed of
ossified vertebrae, while the majority of modern Sharks possess such
vertebrae. Again, the more ancient Crocodilia and Lacertilia have vertebrae
with the articular facets of their centra flattened or biconcave, while
the modern members of the same group have them procoelous. But the most
remarkable examples of progressive modification of the vertebral column,
in correspondence with geological age, are those afforded by the
Pycnodonts among fish, and the Labyrinthodonts among Amphibia.

The late able ichthyologist Heckel pointed out the fact, that, while the
Pycnodonts never possess true vertebral centra, they differ in the degree
of expansion and extension of the ends of the bony arches of the vertebrae
upon the sheath of the notochord; the Carboniferous forms exhibiting
hardly any such expansion, while the Mesozoic genera present a greater
and greater development, until, in the Tertiary forms, the expanded ends
become suturally united so as to form a sort of false vertebra. Hermann
von Meyer, again, to whose luminous researches we are indebted for our
present large knowledge of the organisation of the older Labyrinthodonts,
has proved that the Carboniferous _Archegosaurus_ had very imperfectly
developed vertebral centra, while the Triassic _Mastodonsaurus_ had the
same parts completely ossified.[6]

[Footnote 6: As this Address is passing through the press (March 7,
1862), evidence lies before me of the existence of a new Labyrinthodont
(_Pholidogaster_), from the Edinburgh coal-field with well-ossified
vertebral centra.]

The regularity and evenness of the dentition of the _Anoplotherium_, as
contrasted with that of existing Artiodactyles, and the assumed nearer
approach of the dentition of certain ancient Carnivores to the typical
arrangement, have also been cited as exemplifications of a law of
progressive development, but I know of no other cases based on positive
evidence which are worthy of particular notice.

What then does an impartial survey of the positively ascertained truths
of palaeontology testify in relation to the common doctrines of
progressive modification, which suppose that modification to have taken
place by a necessary progress from more to less embryonic forms, or from
more to less generalised types, within the limits of the period
represented by the fossiliferous rocks?

It negatives those doctrines; for it either shows us no evidence of any
such modification, or demonstrates it to have been very slight; and as to
the nature of that modification, it yields no evidence whatsoever that
the earlier members of any long-continued group were more generalised in
structure than the later ones. To a certain extent, indeed, it may be
said that imperfect ossification of the vertebral column is an embryonic
character; but, on the other hand, it would be extremely incorrect to
suppose that the vertebral columns of the older Vertebrata are in any
sense embryonic in their whole structure.

Obviously, if the earliest fossiliferous rocks now known are coeval with
the commencement of life, and if their contents give us any just
conception of the nature and the extent of the earliest fauna and flora,
the insignificant amount of modification which can be demonstrated to
have taken place in any one group of animals, or plants, is quite
incompatible with the hypothesis that all living forms are the results of
a necessary process of progressive development, entirely comprised within
the time represented by the fossiliferous rocks.

Contrariwise, any admissible hypothesis of progressive modification must
be compatible with persistence without progression, through indefinite
periods. And should such an hypothesis eventually be proved to be true,
in the only way in which it can be demonstrated, viz. by observation and
experiment upon the existing forms of life, the conclusion will
inevitably present itself, that the Palaeozoic Mesozoic, and Cainozoic
faunae and florae, taken together, bear somewhat the same proportion to the
whole series of living beings which have occupied this globe, as the
existing fauna and flora do to them.

Such are the results of palaeontology as they appear, and have for some
years appeared, to the mind of an inquirer who regards that study simply
as one of the applications of the great biological sciences, and who
desires to see it placed upon the same sound basis as other branches of
physical inquiry. If the arguments which have been brought forward are
valid, probably no one, in view of the present state of opinion, will be
inclined to think the time wasted which has been spent upon their
elaboration.



X


GEOLOGICAL REFORM

[1869]

"A great reform in geological speculation seems now to have become
necessary."

"It is quite certain that a great mistake has been made--that British
popular geology at the present time is in direct opposition to the
principles of Natural Philosophy."[1]

[Footnote 1: On Geological Time. By Sir W. Thomson, LL.D. _Transactions
of the Geological Society of Glasgow_, vol. iii.]

In reviewing the course of geological thought during the past year, for
the purpose of discovering those matters to which I might most fitly
direct your attention in the Address which it now becomes my duty to
deliver from the Presidential Chair, the two somewhat alarming sentences
which I have just read, and which occur in an able and interesting essay
by an eminent natural philosopher, rose into such prominence before my
mind that they eclipsed everything else.

It surely is a matter of paramount importance for the British geologists
(some of them very popular geologists too) here in solemn annual session
assembled, to inquire whether the severe judgment thus passed upon them
by so high an authority as Sir William Thomson is one to which they must
plead guilty _sans phrase_, or whether they are prepared to say "not
guilty," and appeal for a reversal of the sentence to that higher court
of educated scientific opinion to which we are all amenable.

As your attorney-general for the time being, I thought I could not do
better than get up the case with a view of advising you. It is true that
the charges brought forward by the other side involve the consideration
of matters quite foreign to the pursuits with which I am ordinarily
occupied; but, in that respect, I am only in the position which is, nine
times out of ten, occupied by counsel, who nevertheless contrive to gain
their causes, mainly by force of mother-wit and common-sense, aided by
some training in other intellectual exercises.

Nerved by such precedents, I proceed to put my pleading before you.

And the first question with which I propose to deal is, What is it to
which Sir W. Thomson refers when he speaks of "geological speculation"
and "British popular geology"?

I find three, more or less contradictory, systems of geological thought,
each of which might fairly enough claim these appellations, standing side
by side in Britain. I shall call one of them CATASTROPHISM, another
UNIFORMITARIANISM, the third EVOLUTIONISM; and I shall try briefly to
sketch the characters of each, that you may say whether the
classification is, or is not, exhaustive.

By CATASTROPHISM, I mean any form of geological speculation which, in
order to account for the phenomena of geology, supposes the operation of
forces different in their nature, or immeasurably different in power,
from those which we at present see in action in the universe.

The Mosaic cosmogony is, in this sense, catastrophic, because it assumes
the operation of extra-natural power. The doctrine of violent upheavals,
_debacles_, and cataclysms in general, is catastrophic, so far as it
assumes that these were brought about by causes which have now no
parallel. There was a time when catastrophism might, pre-eminently, have
claimed the title of "British popular geology"; and assuredly it has yet
many adherents, and reckons among its supporters some of the most
honoured members of this Society.

By UNIFORMITARIANISM, I mean especially, the teaching of Hutton and of
Lyell.

That great though incomplete work, "The Theory of the Earth," seems to me
to be one of the most remarkable contributions to geology which is
recorded in the annals of the science. So far as the not-living world is
concerned, uniformitarianism lies there, not only in germ, but in blossom
and fruit.

If one asks how it is that Hutton was led to entertain views so far in
advance of those prevalent in his time, in some respects; while, in
others, they seem almost curiously limited, the answer appears to me to
be plain.

Hutton was in advance of the geological speculation of his time, because,
in the first place, he had amassed a vast store of knowledge of the facts
of geology, gathered by personal observation in travels of considerable
extent; and because, in the second place, he was thoroughly trained in
the physical and chemical science of his day, and thus possessed, as much
as any one in his time could possess it, the knowledge which is requisite
for the just interpretation of geological phenomena, and the habit of
thought which fits a man for scientific inquiry.

It is to this thorough scientific training that I ascribe Hutton's steady
and persistent refusal to look to other causes than those now in
operation, for the explanation of geological phenomena.

Thus he writes:--"I do not pretend, as he [M. de Luc] does in his theory,
to describe the beginning of things. I take things such as I find them at
present; and from these I reason with regard to that which must have
been."[2]

[Footnote 2: _The Theory of the Earth_, vol. i. p. 173, note.]

And again:--"A theory of the earth, which has for object truth, can have
no retrospect to that which had preceded the present order of the world;
for this order alone is what we have to reason upon; and to reason
without data is nothing but delusion. A theory, therefore, which is
limited to the actual constitution of this earth cannot be allowed to
proceed one step beyond the present order of things."[3]

[Footnote 3: _Ibid._, vol. i. p. 281.]

And so clear is he, that no causes beside such as are now in operation
are needed to account for the character and disposition of the components
of the crust of the earth, that he says, broadly and boldly:--" ... There
is no part of the earth which has not had the same origin, so far as this
consists in that earth being collected at the bottom of the sea, and
afterwards produced, as land, along with masses of melted substances, by
the operation of mineral causes."[4]

[Footnote 4: _Ibid._. p. 371.]

But other influences were at work upon Hutton beside those of a mind
logical by nature, and scientific by sound training; and the peculiar
turn which his speculations took seems to me to be unintelligible, unless
these be taken into account. The arguments of the French astronomers and
mathematicians, which, at the end of the last century, were held to
demonstrate the existence of a compensating arrangement among the
celestial bodies, whereby all perturbations eventually reduced themselves
to oscillations on each side of a mean position, and the stability of the
solar system was secured, had evidently taken strong hold of Hutton's
mind.

In those oddly constructed periods which seem to have prejudiced many
persons against reading his works, but which are full of that peculiar,
if unattractive, eloquence which flows from mastery of the subject,
Hutton says:--

"We have now got to the end of our reasoning; we have no data further to
conclude immediately from that which actually is. But we have got enough;
we have the satisfaction to find, that in Nature there is wisdom, system,
and consistency. For having, in the natural history of this earth, seen a
succession of worlds, we may from this conclude that there is a system in
Nature; in like manner as, from seeing revolutions of the planets, it is
concluded, that there is a system by which they are intended to continue
those revolutions. But if the succession of worlds is established in the
system of nature, it is in vain to look for anything higher in the origin
of the earth. The result, therefore, of this physical inquiry is, that we
find no vestige of a beginning,--no prospect of an end."[5]

[Footnote 5: _Ibid._, vol. i. p. 200.]

Yet another influence worked strongly upon Hutton. Like most philosophers
of his age, he coquetted with those final causes which have been named
barren virgins, but which might be more fitly termed the _hetairoe_ of
philosophy, so constantly have they led men astray. The final cause of
the existence of the world is, for Hutton, the production of life and
intelligence.

"We have now considered the globe of this earth as a machine, constructed
upon chemical as well as mechanical principles, by which its different
parts are all adapted, in form, in quality, and in quantity, to a certain
end; an end attained with certainty or success; and an end from which we
may perceive wisdom, in contemplating the means employed.

"But is this world to be considered thus merely as a machine, to last no
longer than its parts retain their present position, their proper forms
and qualities? Or may it not be also considered as an organised body?
such as has a constitution in which the necessary decay of the machine is
naturally repaired, in the exertion of those productive powers by which
it had been formed.

"This is the view in which we are now to examine the globe; to see if
there be, in the constitution of this world, a reproductive operation, by
which a ruined constitution may be again repaired, and a duration or
stability thus procured to the machine, considered as a world sustaining
plants and animals."[6]

[Footnote 6: _Ibid._, vol. i. pp. 16, 17.]

Kirwan, and the other Philistines of the day, accused Hutton of declaring
that his theory implied that the world never had a beginning, and never
differed in condition from its present state. Nothing could be more
grossly unjust, as he expressly guards himself against any such
conclusion in the following terms:--

"But in thus tracing back the natural operations which have succeeded
each other, and mark to us the course of time past, we come to a period
in which we cannot see any farther. This, however, is not the beginning
of the operations which proceed in time and according to the wise economy
of this world; nor is it the establishing of that which, in the course of
time, had no beginning; it is only the limit of our retrospective view of
those operations which have come to pass in time, and have been conducted
by supreme intelligence."[7]

[Footnote 7: _Ibid._, vol. i. p. 223.]

I have spoken of Uniformitarianism as the doctrine of Hutton and of
Lyell. If I have quoted the older writer rather than the newer, it is
because his works are little known, and his claims on our veneration too
frequently forgotten, not because I desire to dim the fame of his eminent
successor. Few of the present generation of geologists have read
Playfair's "Illustrations," fewer still the original "Theory of the
Earth"; the more is the pity; but which of us has not thumbed every page
of the "Principles of Geology"? I think that he who writes fairly the
history of his own progress in geological thought, will not be able to
separate his debt to Hutton from his obligations to Lyell; and the
history of the progress of individual geologists is the history of
geology.


No one can doubt that the influence of uniformitarian views has been
enormous, and, in the main, most beneficial and favourable to the
progress of sound geology.

Nor can it be questioned that Uniformitarianism has even a stronger title
than Catastrophism to call itself the geological speculation of Britain,
or, if you will, British popular geology. For it is eminently a British
doctrine, and has even now made comparatively little progress on the
continent of Europe. Nevertheless, it seems to me to be open to serious
criticism upon one of its aspects.

I have shown how unjust was the insinuation that Hutton denied a
beginning to the world. But it would not be unjust to say that he
persistently in practice, shut his eyes to the existence of that prior
and different state of things which, in theory, he admitted; and, in this
aversion to look beyond the veil of stratified rocks, Lyell follows him.

Hutton and Lyell alike agree in their indisposition to carry their
speculations a step beyond the period recorded in the most ancient strata
now open to observation in the crust of the earth. This is, for Hutton,
"the point in which we cannot see any farther"; while Lyell tells us,--

"The astronomer may find good reasons for ascribing the earth's form to
the original fluidity of the mass, in times long antecedent to the first
introduction of living beings into the planet; but the geologist must be
content to regard the earliest monuments which it is his task to
interpret, as belonging to a period when the crust had already acquired
great solidity and thickness, probably as great as it now possesses, and
when volcanic rocks, not essentially differing from those now produced,
were formed from time to time, the intensity of volcanic heat being
neither greater nor less than it is now."[8]

[Footnote 8: _Principles of Geology_, vol. ii. p. 211.]

And again, "As geologists, we learn that it is not only the present
condition of the globe which has been suited to the accommodation of
myriads of living creatures, but that many former states also have been
adapted to the organisation and habits of prior races of beings. The
disposition of the seas, continents and islands, and the climates, have
varied; the species likewise have been changed; and yet they have all
been so modelled, on types analogous to those of existing plants and
animals, as to indicate, throughout, a perfect harmony of design and
unity of purpose. To assume that the evidence of the beginning, or end,
of so vast a scheme lies within the reach of our philosophical inquiries,
or even of our speculations, appears to be inconsistent with a just
estimate of the relations which subsist between the finite powers of man
and the attributes of an infinite and eternal Being."[9]

[Footnote 9: _Ibid._, vol. ii. p. 613.]

The limitations implied in these passages appear to me to constitute the
weakness and the logical defect of Uniformitarianism. No one will impute
blame to Hutton that, in face of the imperfect condition, in his day, of
those physical sciences which furnish the keys to the riddles of geology,
he should have thought it practical wisdom to limit his theory to an
attempt to account for "the present order of things"; but I am at a loss
to comprehend why, for all time, the geologist must be content to regard
the oldest fossiliferous rocks as the _ultima Thule_ of his science; or
what there is inconsistent with the relations between the finite and the
infinite mind, in the assumption, that we may discern somewhat of the
beginning, or of the end, of this speck in space we call our earth. The
finite mind is certainly competent to trace out the development of the
fowl within the egg; and I know not on what ground it should find more
difficulty in unravelling the complexities Of the development of the
earth. In fact, as Kant has well remarked,[10] the cosmical process is
really simpler than the biological.

[Footnote 10: "Man darf es sich also nicht befremden lassen, wenn ich
mich unterstehe zu sagen, dass eher die Bildung aller Himmelskoerper, die
Ursache ihrer Bewegungen, kurz der Ursprung der gantzen gegenwaertigen
Verfassung des Weltbaues werden koennen eingesehen werden, ehe die
Erzeugung eines einzigen Krautes oder einer Raupe aus mechanischen
Gruenden, deutlich und vollstaendig kund werden wird."--KANT'S _Saemmtliche
Werke_, Bd. i. p. 220.]

This attempt to limit, at a particular point, the progress of inductive
and deductive reasoning from the things which are, to those which were--
this faithlessness to its own logic, seems to me to have cost
Uniformitarianism the place, as the permanent form of geological
speculation, which it might otherwise have held.

It remains that I should put before you what I understand to be the third
phase of geological speculation--namely, EVOLUTIONISM.

I shall not make what I have to say on this head clear, unless I diverge,
or seem to diverge, for a while, from the direct path of my discourse, so
far as to explain what I take to be the scope of geology itself. I
conceive geology to be the history of the earth, in precisely the same
sense as biology is the history of living beings; and I trust you will
not think that I am overpowered by the influence of a dominant pursuit if
I say that I trace a close analogy between these two histories.

If I study a living being, under what heads does the knowledge I obtain
fall? I can learn its structure, or what we call its ANATOMY; and its
DEVELOPMENT, or the series of changes which it passes through to acquire
its complete structure. Then I find that the living being has certain
powers resulting from its own activities, and the interaction of these
with the activities of other things--the knowledge of which is
PHYSIOLOGY. Beyond this the living being has a position in space and
time, which is its DISTRIBUTION. All these form the body of ascertainable
facts which constitute the _status quo_ of the living creature. But these
facts have their causes; and the ascertainment of these causes is the
doctrine of AETIOLOGY.

If we consider what is knowable about the earth, we shall find that such
earth-knowledge--if I may so translate the word geology--falls into the
same categories.

What is termed stratigraphical geology is neither more nor less than the
anatomy of the earth; and the history of the succession of the formations
is the history of a succession of such anatomies, or corresponds with
development, as distinct from generation.

The internal heat of the earth, the elevation and depression of its
crust, its belchings forth of vapours, ashes, and lava, are its
activities, in as strict a sense as are warmth and the movements and
products of respiration the activities of an animal. The phenomena of the
seasons, of the trade winds, of the Gulf-stream, are as much the results
of the reaction between these inner activities and outward forces, as are
the budding of the leaves in spring and their falling in autumn the
effects of the interaction between the organisation of a plant and the
solar light and heat. And, as the study of the activities of the living
being is called its physiology, so are these phenomena the subject-matter
of an analogous telluric physiology, to which we sometimes give the name
of meteorology, sometimes that of physical geography, sometimes that of
geology. Again, the earth has a place in space and in time, and relations
to other bodies in both these respects, which constitute its
distribution. This subject is usually left to the astronomer; but a
knowledge of its broad outlines seems to me to be an essential
constituent of the stock of geological ideas.

All that can be ascertained concerning the structure, succession of
conditions, actions, and position in space of the earth, is the matter of
fact of its natural history. But, as in biology, there remains the matter
of reasoning from these facts to their causes, which is just as much
science as the other, and indeed more; and this constitutes geological
aetiology.

Having regard to this general scheme of geological knowledge and thought,
it is obvious that geological speculation may be, so to speak, anatomical
and developmental speculation, so far as it relates to points of
stratigraphical arrangement which are out of reach of direct observation;
or, it may be physiological speculation so far as it relates to
undetermined problems relative to the activities of the earth; or, it may
be distributional speculation, if it deals with modifications of the
earth's place in space; or, finally, it will be aetiological speculation
if it attempts to deduce the history of the world, as a whole, from the
known properties of the matter of the earth, in the conditions in which
the earth has been placed.

For the purposes of the present discourse I may take this last to be what
is meant by "geological speculation."

Now Uniformitarianism, as we have seen, tends to ignore geological
speculation in this sense altogether.

The one point the catastrophists and the uniformitarians agreed upon,
when this Society was founded, was to ignore it. And you will find, if
you look back into our records, that our revered fathers in geology
plumed themselves a good deal upon the practical sense and wisdom of this
proceeding. As a temporary measure, I do not presume to challenge its
wisdom; but in all organised bodies temporary changes are apt to produce
permanent effects; and as time has slipped by, altering all the
conditions which may have made such mortification of the scientific flesh
desirable, I think the effect of the stream of cold water which has
steadily flowed over geological speculation within these walls has been
of doubtful beneficence.

The sort of geological speculation to which I am now referring
(geological aetiology, in short) was created, as a science, by that famous
philosopher Immanuel Kant, when, in 1775, he wrote his "General Natural
History and Theory of the Celestial Bodies; or an Attempt to account for
the Constitutional and the Mechanical Origin of the Universe upon
Newtonian principles."[11]

[Footnote 11: Grant (_History of Physical Astronomy_, p. 574) makes but
the briefest reference to Kant.]

In this very remarkable but seemingly little-known treatise,[12] Kant
expounds a complete cosmogony, in the shape of a theory of the causes
which have led to the development of the universe from diffused atoms of
matter endowed with simple attractive and repulsive forces.

[Footnote 12: "Allgemeine Naturgeschichte und Theorie des Himmels; oder
Versuch von der Verfassung und dem mechanischen Ursprunge des ganzen
Weltgebaeudes nach Newton'schen Grundsatzen abgehandelt."--KANT'S
_Saemmtliche Werke_, Bd. i. p. 207.]

"Give me matter," says Kant, "and I will build the world;" and he
proceeds to deduce from the simple data from which he starts, a doctrine
in all essential respects similar to the well-known "Nebular Hypothesis"
of Laplace.[13] He accounts for the relation of the masses and the
densities of the planets to their distances from the sun, for the
eccentricities of their orbits, for their rotations, for their
satellites, for the general agreement in the direction of rotation among
the celestial bodies, for Saturn's ring, and for the zodiacal light. He
finds in each system of worlds, indications that the attractive force of
the central mass will eventually destroy its organisation, by
concentrating upon itself the matter of the whole system; but, as the
result of this concentration, he argues for the development of an amount
of heat which will dissipate the mass once more into a molecular chaos
such as that in which it began.

[Footnote 13: _Systeme du Monde_, tome ii. chap. 6.]

Kant pictures to himself the universe as once an infinite expansion of
formless and diffused matter. At one point of this he supposes a single
centre of attraction set up; and, by strict deductions from admitted
dynamical principles, shows how this must result in the development of a
prodigious central body, surrounded by systems of solar and planetary
worlds in all stages of development. In vivid language he depicts the
great world-maelstrom, widening the margins of its prodigious eddy in the
slow progress of millions of ages, gradually reclaiming more and more of
the molecular waste, and converting chaos into cosmos. But what is gained
at the margin is lost in the centre; the attractions of the central
systems bring their constituents together, which then, by the heat
evolved, are converted once more into molecular chaos. Thus the worlds
that are, lie between the ruins of the worlds that have been, and the
chaotic materials of the worlds that shall be; and in spite of all waste
and destruction, Cosmos is extending his borders at the expense of Chaos.

Kant's further application of his views to the earth itself is to be
found in his "Treatise on Physical Geography"[14] (a term under which the
then unknown science of geology was included), a subject which he had
studied with very great care and on which he lectured for many years. The
fourth section of the first part of this Treatise is called "History of
the great Changes which the Earth has formerly undergone and is still
undergoing," and is, in fact, a brief and pregnant essay upon the
principles of geology. Kant gives an account first "of the gradual
changes which are now taking place" under the heads of such as are caused
by earthquakes, such as are brought about by rain and rivers, such as are
effected by the sea, such as are produced by winds and frost; and,
finally, such as result from the operations of man.

[Footnote 14: Kant's _Saemmtliche Werke_, Bd. viii. p. 145.]

The second part is devoted to the "Memorials of the Changes which the
Earth has undergone in remote Antiquity." These are enumerated as:--A.
Proofs that the sea formerly covered the whole earth. B. Proofs that the
sea has often been changed into dry land and then again into sea. C. A
discussion of the various theories of the earth put forward by
Scheuchzer, Moro, Bonnet, Woodward, White, Leibnitz, Linnaeus, and Buffon.

The third part contains an "Attempt to give a sound explanation of the
ancient history of the earth."

I suppose that it would be very easy to pick holes in the details of
Kant's speculations, whether cosmological, or specially telluric, in
their application. But for all that, he seems to me to have been the
first person to frame a complete system of geological speculation by
founding the doctrine of evolution.

With as much truth as Hutton, Kant could say, "I take things just as I
find them at present, and, from these, I reason with regard to that which
must have been." Like Hutton, he is never tired of pointing out that "in
Nature there is wisdom, system, and consistency." And, as in these great
principles, so in believing that the cosmos has a reproductive operation
"by which a ruined constitution may be repaired," he forestalls Hutton;
while, on the other hand, Kant is true to science. He knows no bounds to
geological speculation but those of the intellect. He reasons back to a
beginning of the present state of things; he admits the possibility of an
end.

I have said that the three schools of geological speculation which I have
termed Catastrophism, Uniformitarianism, and Evolutionism, are commonly
supposed to be antagonistic to one another; and I presume it will have
become obvious that in my belief, the last is destined to swallow up the
other two. But it is proper to remark that each of the latter has kept
alive the tradition of precious truths.

CATASTROPHISM has insisted upon the existence of a practically unlimited
bank of force, on which the theorist might draw; and it has cherished the
idea of the development of the earth from a state in which its form, and
the forces which it exerted, were very different from those we now know.
That such difference of form and power once existed is a necessary part
of the doctrine of evolution.

UNIFORMITARIANISM, on the other hand, has with equal justice insisted
upon a practically unlimited bank of time, ready to discount any quantity
of hypothetical paper. It has kept before our eyes the power of the
infinitely little, time being granted, and has compelled us to exhaust
known causes, before flying to the unknown.

To my mind there appears to be no sort of necessary theoretical
antagonism between Catastrophism and Uniformitarianism. On the contrary,
it is very conceivable that catastrophes may be part and parcel of
uniformity. Let me illustrate my case by analogy. The working of a clock
is a model of uniform action; good time-keeping means uniformity of
action. But the striking of the clock is essentially a catastrophe; the
hammer might be made to blow up a barrel of gunpowder, or turn on a
deluge of water; and, by proper arrangement, the clock, instead of
marking the hours, might strike at all sorts of irregular periods, never
twice alike, in the intervals, force, or number of its blows.
Nevertheless, all these irregular, and apparently lawless, catastrophes
would be the result of an absolutely uniformitarian action; and we might
have two schools of clock-theorists, one studying the hammer and the
other the pendulum.

Still less is there any necessary antagonists between either of these
doctrines and that of Evolution, which embraces all that is sound in both
Catastrophism and Uniformitarianism, while it rejects the arbitrary
assumptions of the one and the, as arbitrary, limitations of the other.
Nor is the value of the doctrine of Evolution to the philosophic thinker
diminished by the fact that it applies the same method to the living and
the not-living world; and embraces, in one stupendous analogy, the growth
of a solar system from molecular chaos, the shaping of the earth from the
nebulous cub-hood of its youth, through innumerable changes and
immeasurable ages, to its present form; and the development of a living
being from the shapeless mass of protoplasm we term a germ.

I do not know whether Evolutionism can claim that amount of currency
which would entitle it to be called British popular geology; but, more or
less vaguely, it is assuredly present in the minds of most geologists.

Such being the three phases of geological speculation, we are now in
position to inquire which of these it is that Sir William Thomson calls
upon us to reform in the passages which I have cited.

It is obviously Uniformitarianism which the distinguished physicist takes
to be the representative of geological speculation in general. And thus a
first issue is raised, inasmuch as many persons (and those not the least
thoughtful among the younger geologists) do not accept strict
Uniformitarianism as the final form of geological speculation. We should
say, if Hutton and Playfair declare the course of the world to have been
always the same, point out the fallacy by all means; but, in so doing, do
not imagine that you are proving modern geology to be in opposition to
natural philosophy. I do not suppose that, at the present day, any
geologist would be found to maintain absolute Uniformitarianism, to deny
that the rapidity of the rotation of the earth _may_ be diminishing, that
the sun _may_ be waxing dim, or that the earth itself _may_ be cooling.
Most of us, I suspect, are Gallios, "who care for none of these things,"
being of opinion that, true or fictitious, they have made no practical
difference to the earth, during the period of which a record is preserved
in stratified deposits.

The accusation that we have been running counter to the _principles_ of
natural philosophy, therefore, is devoid of foundation. The only question
which can arise is whether we have, or have not, been tacitly making
assumptions which are in opposition to certain conclusions which may be
drawn from those principles. And this question subdivides itself into
two:--the first, are we really contravening such conclusions? the second,
if we are, are those conclusions so firmly based that we may not
contravene them? I reply in the negative to both these questions, and I
will give you my reasons for so doing. Sir William Thomson believes that
he is able to prove, by physical reasonings, "that the existing state of
things on the earth, life on the earth--all geological history showing
continuity of life--must be limited within some such period of time as
one hundred million years" (_loc. cit._ p. 25).

The first inquiry which arises plainly is, has it ever been denied that
this period _may_ be enough for the purposes of geology?

The discussion of this question is greatly embarrassed by the vagueness
with which the assumed limit is, I will not say defined, but indicated,--
"some such period of past time as one hundred million years." Now does
this mean that it may have been two, or three, or four hundred million
years? Because this really makes all the difference.[15]

[Footnote 15: Sir William Thomson implies (_loc. cit_. p. 16) that the
precise time is of no consequence: "the principle is the same"; but, as
the principle is admitted, the whole discussion turns on its practical
results.]

I presume that 100,000 feet may be taken as a full allowance for the
total thickness of stratified rocks containing traces of life; 100,000
divided by 100,000,000 = 0.001. Consequently, the deposit of 100,000 feet
of stratified rock in 100,000,000 years means that the deposit has taken
place at the rate of 1/1000 of a foot, or, say, 1/83 of an inch, per
annum.

Well, I do not know that any one is prepared to maintain that, even
making all needful allowances, the stratified rocks may not have been
formed, on the average, at the rate of 1/83 of an inch per annum. I
suppose that if such could be shown to be the limit of world-growth, we
could put up with the allowance without feeling that our speculations had
undergone any revolution. And perhaps, after all, the qualifying phrase
"some such period" may not necessitate the assumption of more than 1/166
or 1/249 or 1/332 of an inch of deposit per year, which, of course, would
give us still more ease and comfort.

But, it may be said, that it is biology, and not geology, which asks for
so much time--that the succession of life demands vast intervals; but
this appears to me to be reasoning in a circle. Biology takes her time
from geology. The only reason we have for believing in the slow rate of
the change in living forms is the fact that they persist through a series
of deposits which, geology informs us, have taken a long while to make.
If the geological clock is wrong, all the naturalist will have to do is
to modify his notions of the rapidity of change accordingly. And I
venture to point out that, when we are told that the limitation of the
period during which living beings have inhabited this planet to one, two,
or three hundred million years requires a complete revolution in
geological speculation, the _onus probandi_ rests on the maker of the
assertion, who brings forward not a shadow of evidence in its support.

Thus, if we accept the limitation of time placed before us by Sir W.
Thomson, it is not obvious, on the face of the matter, that we shall have
to alter, or reform, our ways in any appreciable degree; and we may
therefore proceed with much calmness, and indeed much indifference, as to
the result, to inquire whether that limitation is justified by the
arguments employed in its support.

These arguments are three in number.--

I. The first is based upon the undoubted fact that the tides tend to
<DW44> the rate of the earth's rotation upon its axis. That this must be
so is obvious, if one considers, roughly, that the tides result from the
pull which the sun and the moon exert upon the sea, causing it to act as
a sort of break upon the rotating solid earth.

Kant, who was by no means a mere "abstract philosopher," but a good
mathematician and well versed in the physical science of his time, not
only proved this in an essay of exquisite clearness and intelligibility,
now more than a century old,[16] but deduced from it some of its more
important consequences, such as the constant turning of one face of the
moon towards the earth.

[Footnote 16: "Untersuchung der Frage oh die Erde in ihrer Umdrehung um
die Achse, wodurch sie die Abwechselung des Tages und der Nacht
hervorbringt, einige Veraenderung seit den ersten Zeiten ihres Ursprunges
erlitten habe, &c."--KANT's _Saemmntliche Werke_, Bd. i. p. 178.]

But there is a long step from the demonstration of a tendency to the
estimation of the practical value of that tendency, which is all with
which we are at present concerned. The facts bearing on this point appear
to stand as follows:--

It is a matter of observation that the moon's mean motion is (and has for
the last 3,000 years been) undergoing an acceleration, relatively to the
rotation of the earth. Of course this may result from one of two causes:
the moon may really have been moving more swiftly in its orbit; or the
earth may have been rotating more slowly on its axis.

Laplace believed he had accounted for this phenomenon by the fact that
the eccentricity of the earth's orbit has been diminishing throughout
these 3,000 years. This would produce a diminution of the mean attraction
of the sun on the moon; or, in other words, an increase in the attraction
of the earth on the moon; and, consequently, an increase in the rapidity
of the orbital motion of the latter body. Laplace, therefore, laid the
responsibility of the acceleration upon the moon, and if his views were
correct, the tidal retardation must either be insignificant in amount, or
be counteracted by some other agency.

Our great astronomer, Adams, however, appears to have found a flaw in
Laplace's calculation, and to have shown that only half the observed
retardation could be accounted for in the way he had suggested. There
remains, therefore, the other half to be accounted for; and here, in the
absence of all positive knowledge, three sets of hypotheses have been
suggested.

(_a_.) M. Delaunay suggests that the earth is at fault, in consequence of
the tidal retardation. Messrs. Adams, Thomson, and Tait work out this
suggestion, and, "on a certain assumption as to the proportion of
retardations due to the sun and moon," find the earth may lose twenty-two
seconds of time in a century from this cause.[17]

[Footnote 17: Sir W. Thomson, _loc. cit_. p. 14.]

(_b_.) But M. Dufour suggests that the retardation of the earth (which is
hypothetically assumed to exist) may be due in part, or wholly, to the
increase of the moment of inertia of the earth by meteors falling upon
its surface. This suggestion also meets with the entire approval of Sir
W. Thomson, who shows that meteor-dust, accumulating at the rate of one
foot in 4,000 years, would account for the remainder of retardation.[18]

[Footnote 18: _Ibid._ p. 27.]

(_c_.) Thirdly, Sir W. Thomson brings forward an hypothesis of his own
with respect to the cause of the hypothetical retardation of the earth's
rotation:--

"Let us suppose ice to melt from the polar regions (20 deg. round each pole,
we may say) to the extent of something more than a foot thick, enough to
give 1.1 foot of water over those areas, or 0.006 of a foot of water if
spread over the whole globe, which would, in reality, raise the sea-level
by only some such undiscoverable difference as three-fourths of an inch
or an inch. This, or the reverse, which we believe might happen any year,
and could certainly not be detected without far more accurate
observations and calculations for the mean sea-level than any hitherto
made, would slacken or quicken the earth's rate as a timekeeper by one-
tenth of a second per year."[19]

[Footnote 19: _Ibid._]

I do not presume to throw the slightest doubt upon the accuracy of any of
the calculations made by such distinguished mathematicians as those who
have made the suggestions I have cited. On the contrary, it is necessary
to my argument to assume that they are all correct. But I desire to point
out that this seems to be one of the many cases in which the admitted
accuracy of mathematical process is allowed to throw a wholly
inadmissible appearance of authority over the results obtained by them.
Mathematics may be compared to a mill of exquisite workmanship, which
grinds you stuff of any degree of fineness; but, nevertheless, what you
get out depends upon what you put in; and as the grandest mill in the
world will not extract wheat-flour from peascods, so pages of formulae
will not get a definite result out of loose data.

In the present instance it appears to be admitted:--

1. That it is not absolutely certain, after all, whether the moon's mean
motion is undergoing acceleration, or the earth's rotation
retardation.[20] And yet this is the key of the whole position.

[Footnote 20: It will be understood that I do not wish to deny that the
earth's rotation _may be_ undergoing retardation.]

2. If the rapidity of the earth's rotation is diminishing, it is not
certain how much of that retardation is due to tidal friction, how much
to meteors, how much to possible excess of melting over accumulation of
polar ice, during the period covered by observation, which amounts, at
the outside, to not more than 2,600 years.

3. The effect of a different distribution of land and water in modifying
the retardation caused by tidal friction, and of reducing it, under some
circumstances, to a minimum, does not appear to be taken into account.

4. During the Miocene epoch the polar ice was certainly many feet thinner
than it has been during, or since, the Glacial epoch. Sir W. Thomson
tells us that the accumulation of something more than a foot of ice
around the poles (which implies the withdrawal of, say, an inch of water
from the general surface of the sea) will cause the earth to rotate
quicker by one-tenth of a second per annum. It would appear, therefore,
that the earth may have been rotating, throughout the whole period which
has elapsed from the commencement of the Glacial epoch down to the
present time, one, or more, seconds per annum quicker than it rotated
during the Miocene epoch.

But, according to Sir W. Thomson's calculation, tidal retardation will
only account for a retardation of 22" in a century, or 22/100 (say 1/5)
of a second per annum.

Thus, assuming that the accumulation of polar ice since the Miocene epoch
has only been sufficient to produce ten times the effect of a coat of ice
one foot thick, we shall have an accelerating cause which covers all the
loss from tidal action, and leaves a balance of 4/5 of a second per annum
in the way of acceleration.

If tidal retardation can be thus checked and overthrown by other
temporary conditions, what becomes of the confident assertion, based upon
the assumed uniformity of tidal retardation, that ten thousand million
years ago the earth must have been rotating more than twice as fast as at
present, and, therefore, that we geologists are "in direct opposition to
the principles of Natural Philosophy" if we spread geological history
over that time?

II. The second argument is thus stated by Sir W. Thomson:--"An article,
by myself, published in 'Macmillan's Magazine' for March 1862, on the age
of the sun's heat, explains results of investigation into various
questions as to possibilities regarding the amount of heat that the sun
could have, dealing with it as you would with a stone, or a piece of
matter, only taking into account the sun's dimensions, which showed it to
be possible that the sun may have already illuminated the earth for as
many as one hundred million years, but at the same time rendered it
almost certain that he had not illuminated the earth for five hundred
millions of years. The estimates here are necessarily very vague; but
yet, vague as they are, I do not know that it is possible, upon any
reasonable estimate founded on known properties of matter, to say that we
can believe the sun has really illuminated the earth for five hundred
million years."[21]

[Footnote 21: _Loc. cit._ p. 20.]

I do not wish to "Hansardise" Sir William Thomson by laying much stress
on the fact that, only fifteen years ago he entertained a totally
different view of the origin of the sun's heat, and believed that the
energy radiated from year to year was supplied from year to year--a
doctrine which would have suited Hutton perfectly. But the fact that so
eminent a physical philosopher has, thus recently, held views opposite to
those which he now entertains, and that he confesses his own estimates to
be "very vague," justly entitles us to disregard those estimates, if any
distinct facts on our side go against them. However, I am not aware that
such facts exist. As I have already said, for anything I know, one, two,
or three hundred millions of years may serve the needs of geologists
perfectly well.

III. The third line of argument is based upon the temperature of the
interior of the earth. Sir W. Thomson refers to certain investigations
which prove that the present thermal condition of the interior of the
earth implies either a heating of the earth within the last 20,000 years
of as much as 100 deg. F., or a greater heating all over the surface at some
time further back than 20,000 years, and then proceeds thus:--

"Now, are geologists prepared to admit that, at some time within the last
20,000 years, there has been all over the earth so high a temperature as
that? I presume not; no geologist--no _modern_ geologist--would for a
moment admit the hypothesis that the present state of underground heat is
due to a heating of the surface at so late a period as 20,000 years ago.
If that is not admitted we are driven to a greater heat at some time more
than 20,000 years ago. A greater heating all over the surface than 100 deg.
Fahrenheit would kill nearly all existing plants and animals, I may
safely say. Are modern geologists prepared to say that all life was
killed off the earth 50,000, 100,000, or 200,000 years ago? For the
uniformity theory, the further back the time of high surface-temperature
is put the better; but the further back the time of heating, the hotter
it must have been. The best for those who draw most largely on time is
that which puts it furthest back; and that is the theory that the heating
was enough to melt the whole. But even if it was enough to melt the
whole, we must still admit some limit, such as fifty million years, one
hundred million years, or two or three hundred million years ago. Beyond
that we cannot go."[22]

[Footnote 22: _Loc. cit._ p. 24.]

It will be observed that the "limit" is once again of the vaguest,
ranging from 50,000,000 years to 300,000,000. And the reply is, once
more, that, for anything that can be proved to the contrary, one or two
hundred million years might serve the purpose, even of a thoroughgoing
Huttonian uniformitarian, very well.

But if, on the other hand, the 100,000,000 or 200,000,000 years appear to
be insufficient for geological purposes, we must closely criticise the
method by which the limit is reached. The argument is simple enough.
_Assuming_ the earth to be nothing but a cooling mass, the quantity of
heat lost per year, _supposing_ the rate of cooling to have been uniform,
multiplied by any given number of years, will be given the minimum
temperature that number of years ago.

But is the earth nothing but a cooling mass, "like a hot-water jar such
as is used in carriages," or "a globe of sandstone," and has its cooling
been uniform? An affirmative answer to both these questions seems to be
necessary to the validity of the calculations on which Sir W. Thomson
lays so much stress.

Nevertheless it surely may be urged that such affirmative answers are
purely hypothetical, and that other suppositions have an equal right to
consideration.

For example, is it not possible that, at the prodigious temperature which
would seem to exist at 100 miles below the surface, all the metallic
bases may behave as mercury does at a red heat, when it refuses to
combine with oxygen; while, nearer the surface, and therefore at a lower
temperature, they may enter into combination (as mercury does with oxygen
a few degrees below its boiling-point), and so give rise to a heat
totally distinct from that which they possess as cooling bodies? And has
it not also been proved by recent researches that the quality of the
atmosphere may immensely affect its permeability to heat; and,
consequently, profoundly modify the rate of cooling the globe as a whole?

I do not think it can be denied that such conditions may exist, and may
so greatly affect the supply, and the loss, of terrestrial heat as to
destroy the value of any calculations which leave them out of sight.

My functions as your advocate are at an end. I speak with more than the
sincerity of a mere advocate when I express the belief that the case
against us has entirely broken down. The cry for reform which has been
raised without, is superfluous, inasmuch as we have long been reforming
from within, with all needful speed. And the critical examination of the
grounds upon which the very grave charge of opposition to the principles
of Natural Philosophy has been brought against us, rather shows that we
have exercised a wise discrimination in declining, for the present, to
meddle with our foundations.



XI


PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION

[1870]

It is now eight years since, in the absence of the late Mr. Leonard
Horner, who then presided over us, it fell to my lot, as one of the
Secretaries of this Society, to draw up the customary Annual Address. I
availed myself of the opportunity to endeavour to "take stock" of that
portion of the science of biology which is commonly called
"palaeontology," as it then existed; and, discussing one after another the
doctrines held by palaeontologists, I put before you the results of my
attempts to sift the well-established from the hypothetical or the
doubtful. Permit me briefly to recall to your minds what those results
were:--

1. The living population of all parts of the earth's surface which have
yet been examined has undergone a succession of changes which, upon the
whole, have been of a slow and gradual character.

2. When the fossil remains which are the evidences of these successive
changes, as they have occurred in any two more or less distant parts of
the surface of the earth, are compared, they exhibit a certain broad and
general parallelism. In other words, certain forms of life in one
locality occur in the same general order of succession as, or are
_homotaxial_ with, similar forms in the other locality.

3. Homotaxis is not to be held identical with synchronism without
independent evidence. It is possible that similar, or even identical,
faunae and florae in two different localities may be of extremely different
ages, if the term "age" is used in its proper chronological sense. I
stated that "geographical provinces, or zones, may have been as
distinctly marked in the Palaeozoic epoch as at present; and those
seemingly sudden appearances of new genera and species which we ascribe
to new creation, may be simple results of migration."

4. The opinion that the oldest known fossils are the earliest forms of
life has no solid foundation.

5. If we confine ourselves to positively ascertained facts, the total
amount of change in the forms of animal and vegetable life, since the
existence of such forms is recorded, is small. When compared with the
lapse of time since the first appearance of these forms, the amount of
change is wonderfully small. Moreover, in each great group of the animal
and vegetable kingdoms, there are certain forms which I termed PERSISTENT
TYPES, which have remained, with but very little apparent change, from
their first appearance to the present time.

6. In answer to the question "What, then, does an impartial survey of the
positively ascertained truths of palaeontology testify in relation to the
common doctrines of progressive modification, which suppose that
modification to have taken place by a necessary progress from more to
less embryonic forms, from more to less generalised types, within the
limits of the period represented by the fossiliferous rocks?" I reply,
"It negatives these doctrines; for it either shows us no evidence of such
modification, or demonstrates such modification as has occurred to have
been very slight; and, as to the nature of that modification, it yields
no evidence whatsoever that the earlier members of any long-continued
group were more generalised in structure than the later ones."

I think that I cannot employ my last opportunity of addressing you,
officially, more properly--I may say more dutifully--than in revising
these old judgments with such help as further knowledge and reflection,
and an extreme desire to get at the truth, may afford me.

1. With respect to the first proposition, I may remark that whatever may
be the case among the physical geologists, catastrophic palaeontologists
are practically extinct. It is now no part of recognised geological
doctrine that the species of one formation all died out and were replaced
by a brand-new set in the next formation. On the contrary, it is
generally, if not universally, agreed that the succession of life has
been the result of a slow and gradual replacement of species by species;
and that all appearances of abruptness of change are due to breaks in the
series of deposits, or other changes in physical conditions. The
continuity of living forms has been unbroken from the earliest times to
the present day.

2, 3. The use of the word "homotaxis" instead of "synchronism" has not,
so far as I know, found much favour in the eyes of geologists. I hope,
therefore, that it is a love for scientific caution, and not mere
personal affection for a bantling of my own, which leads me still to
think that the change of phrase is of importance, and that the sooner it
is made, the sooner shall we get rid of a number of pitfalls which beset
the reasoner upon the facts and theories of geology.

One of the latest pieces of foreign intelligence which has reached us is
the information that the Austrian geologists have, at last, succumbed to
the weighty evidence which M. Barrande has accumulated, and have admitted
the doctrine of colonies. But the admission of the doctrine of colonies
implies the further admission that even identity of organic remains is no
proof of the synchronism of the deposits which contain them.

4. The discussions touching the _Eozoon,_ which commenced in 1864, have
abundantly justified the fourth proposition. In 1862, the oldest record
of life was in the Cambrian rocks; but if the _Eozoon_ be, as Principal
Dawson and Dr. Carpenter have shown so much reason for believing, the
remains of a living being, the discovery of its true nature carried life
back to a period which, as Sir William Logan has observed, is as remote
from that during which the Cambrian rocks were deposited, as the Cambrian
epoch itself is from the tertiaries. In other words, the ascertained
duration of life upon the globe was nearly doubled at a stroke.

5. The significance of persistent types, and of the small amount of
change which has taken place even in those forms which can be shown to
have been modified, becomes greater and greater in my eyes, the longer I
occupy myself with the biology of the past.

Consider how long a time has elapsed since the Miocene epoch. Yet, at
that time there is reason to believe that every important group in every
order of the _Mammalia_ was represented. Even the comparatively scanty
Eocene fauna yields examples of the orders _Cheiroptera, Insectivora,
Rodentia_, and _Perissodactyla_; of _Artiodactyla_ under both the
Ruminant and the Porcine modifications; of _Caranivora, Cetacea_, and
_Marsupialia_.

Or, if we go back to the older half of the Mesozoic epoch, how truly
surprising it is to find every order of the _Reptilia_, except the
_Ophidia_, represented; while some groups, such as the _Ornithoseclida_
and the _Pterosauria_, more specialised than any which now exist,
abounded.

There is one division of the _Amphibia_ which offers especially important
evidence upon this point, inasmuch as it bridges over the gap between the
Mesozoic and the Palaeozoic formations (often supposed to be of such
prodigious magnitude), extending, as it does, from the bottom of the
Carboniferous series to the top of the Trias, if not into the Lias. I
refer to the Labyrinthodonts. As the Address of 1862 was passing through
the press, I was able to mention, in a note, the discovery of a large
Labyrinthodont, with well-ossified vertebrae, in the Edinburgh coal-field.
Since that time eight or ten distinct genera of Labyrinthodonts have been
discovered in the Carboniferous rocks of England, Scotland, and Ireland,
not to mention the American forms described by Principal Dawson and
Professor Cope. So that, at the present time, the Labyrinthodont Fauna of
the Carboniferous rocks is more extensive and diversified than that of
the Trias, while its chief types, so far as osteology enables us to
judge, are quite as highly organised. Thus it is certain that a
comparatively highly organised vertebrate type, such as that of the
Labyrinthodonts, is capable of persisting, with no considerable change,
through the period represented by the vast deposits which constitute the
Carboniferous, the Permian, and the Triassic formations.

The very remarkable results which have been brought to light by the
sounding and dredging operations, which have been carried on with such
remarkable success by the expeditions sent out by our own, the American,
and the Swedish Governments, under the supervision of able naturalists,
have a bearing in the same direction. These investigations have
demonstrated the existence, at great depths in the ocean, of living
animals in some cases identical with, in others very similar to, those
which are found fossilised in the white chalk. The _Globigerinoe_,
Cyatholiths, Coccospheres, Discoliths in the one are absolutely identical
with those in the other; there are identical, or closely analogous,
species of Sponges, Echinoderms, and Brachiopods. Off the coast of
Portugal, there now lives a species of _Beryx_, which, doubtless, leaves
its bones and scales here and there in the Atlantic ooze, as its
predecessor left its spoils in the mud of the sea of the Cretaceous
epoch.

Many years ago[1] I ventured to speak of the Atlantic mud as "modern
chalk," and I know of no fact inconsistent with the view which Professor
Wyville Thomson has advocated, that the modern chalk is not only the
lineal descendant of the ancient chalk, but that it remains, so to speak,
in the possession of the ancestral estate; and that from the Cretaceous
period (if not much earlier) to the present day, the deep sea has covered
a large part of what is now the area of the Atlantic. But if
_Globigerina_, and _Terebratula caput-serpentis_ and _Beryx_, not to
mention other forms of animals and of plants, thus bridge over the
interval between the present and the Mesozoic periods, is it possible
that the majority of other living things underwent a "sea-change into
something new and strange" all at once?

[Footnote 1: See an article in the _Saturday Review_, for 1858, on
"Chalk, Ancient and Modern."]

6. Thus far I have endeavoured to expand and to enforce by fresh
arguments, but not to modify in any important respect, the ideas
submitted to you on a former occasion. But when I come to the
propositions touching progressive modification, it appears to me, with
the help of the new light which has broken from various quarters, that
there is much ground for softening the somewhat Brutus-like severity with
which, in 1862, I dealt with a doctrine, for the truth of which I should
have been glad enough to be able to find a good foundation. So far,
indeed, as the _Invertebrata_ and the lower _Vertebrata_ are concerned,
the facts and the conclusions which are to be drawn from them appear to
me to remain what they were. For anything that, as yet, appears to the
contrary, the earliest known Marsupials may have been as highly organised
as their living congeners; the Permian lizards show no signs of
inferiority to those of the present day; the Labyrinthodonts cannot be
placed below the living Salamander and Triton; the Devonian Ganoids are
closely related to _Polypterus_ and to _Lepidosiren_.

But when we turn to the higher _Vertebrata_, the results of recent
investigations, however we may sift and criticise them, seem to me to
leave a clear balance in favour of the doctrine of the evolution of
living forms one from another. Nevertheless, in discussing this question,
it is very necessary to discriminate carefully between the different
kinds of evidence from fossil remains which are brought forward in favour
of evolution.

Every fossil which takes an intermediate place between forms of life
already known, may be said, so far as it is intermediate, to be evidence
in favour of evolution, inasmuch as it shows a possible road by which
evolution may have taken place. But the mere discovery of such a form
does not, in itself, prove that evolution took place by and through it,
nor does it constitute more than presumptive evidence in favour of
evolution in general. Suppose A, B, C to be three forms, while B is
intermediate in structure between A and C. Then the doctrine of evolution
offers four possible alternatives. A may have become C by way of B; or C
may have become A by way of B; or A and C may be independent
modifications of B; or A, B, and C may be independent modifications of
some unknown D. Take the case of the Pigs, the _Anoplothcridoe_, and the
Ruminants. The _Anoplothcridoe_ are intermediate between the first and
the last; but this does not tell us whether the Ruminants have come from
the Pigs, or the Pigs from Ruminants, or both from _Anoplothcridoe_, or
whether Pigs, Ruminants, and _Anoplotlicridoe_ alike may not have
diverged from some common stock.

But if it can be shown that A, B, and C exhibit successive stages in the
degree of modification, or specialisation, of the same type; and if,
further, it can be proved that they occur in successively newer deposits,
A being in the oldest and C in the newest, then the intermediate
character of B has quite another importance, and I should accept it,
without hesitation, as a link in the genealogy of C. I should consider
the burden of proof to be thrown upon any one who denied C to have been
derived from A by way of B, or in some closely analogous fashion; for it
is always probable that one may not hit upon the exact line of filiation,
and, in dealing with fossils, may mistake uncles and nephews for fathers
and sons.

I think it necessary to distinguish between the former and the latter
classes of intermediate forms, as _intercalary types_ and _linear types_.
When I apply the former term, I merely mean to say that as a matter of
fact, the form B, so named, is intermediate between the others, in the
sense in which the _Anoplotherium_ is intermediate between the Pigs and
the Ruminants--without either affirming, or denying, any direct genetic
relation between the three forms involved. When I apply the latter term,
on the other hand, I mean to express the opinion that the forms A, B, and
C constitute a line of descent, and that B is thus part of the lineage of
C.

From the time when Cuvier's wonderful researches upon the extinct Mammals
of the Paris gypsum first made intercalary types known, and caused them
to be recognised as such, the number of such forms has steadily increased
among the higher _Mammalia_. Not only do we now know numerous intercalary
forins of _Ungulata_, but M. Gaudry's great monograph upon the fossils of
Pikermi (which strikes me as one of the most perfect pieces of
palaeontological work I have seen for a long time) shows us, among the
Primates, _Mesopithecus_ as an intercalary form between the
_Semnopitheci_ and the _Macaci_; and among the _Carnivora_, _Hyoenictis_
and _Ictitherium_ as intercalary, or, perhaps, linear types between the
_Viverridoe_ and the _Hyoenidoe_.

Hardly any order of the higher _Mammalia_ stands so apparently separate
and isolated from the rest as that of the _Cetacea_; though a careful
consideration of the structure of the pinnipede _Carnivora_, or Seals,
shows, in them, many an approximation towards the still more completely
marine mammals. The extinct _Zeuglodon_, however, presents us with an
intercalary form between the type of the Seals and that of the Whales.
The skull of this great Eocene sea-monster, in fact, shows by the narrow
and prolonged interorbital region; the extensive union of the parietal
bones in a sagittal suture; the well-developed nasal bones; the distinct
and large incisors implanted in premaxillary bones, which take a full
share in bounding the fore part of the gape; the two-fanged molar teeth
with triangular and serrated crowns, not exceeding five on each side in
each jaw; and the existence of a deciduous dentition--its close relation
with the Seals. While, on the other hand, the produced rostral form of
the snout, the long symphysis, and the low coronary process of the
mandible are approximations to the cetacean form of those parts.

The scapula resembles that of the cetacean _Hyperoodon_, but the supra-
spinous fossa is larger and more seal-like; as is the humerus, which
differs from that of the _Cetacea_ in presenting true articular surfaces
for the free jointing of the bones of the fore-arm. In the apparently
complete absence of hinder limbs, and in the characters of the vertebral
column, the _Zeuglodon_ lies on the cetacean side of the boundary line;
so that upon the whole, the Zeuglodonts, transitional as they are, are
conveniently retained in the cetacean order. And the publication, in
1864, of M. Van Beneden's memoir on the Miocene and Pliocene _Squalodon_,
furnished much better means than anatomists previously possessed of
fitting in another link of the chain which connects the existing
_Cetacea_ with _Zeuglodon_. The teeth are much more numerous, although
the molars exhibit the zeuglodont double fang; the nasal bones are very
short, and the upper surface of the rostrum presents the groove, filled
up during life by the prolongation of the ethmoidal cartilage, which is
so characteristic of the majority of the _Cetacea_.

It appears to me that, just as among the existing _Carnivora_, the
walruses and the eared seals are intercalary forms between the fissipede
Carnivora and the ordinary seals, so the Zeuglodonts are intercalary
between the _Carnivora_, as a whole, and the _Cetacea_. Whether the
Zeuglodonts are also linear types in their relation to these two groups
cannot be ascertained, until we have more definite knowledge than we
possess at present, respecting the relations in time of the _Carnivora_
and _Cetacea_.

Thus far we have been concerned with the intercalary types which occupy
the intervals between Families or Orders of the same class; but the
investigations which have been carried on by Professor Gegenbaur,
Professor Cope, and myself into the structure and relations of the
extinct reptilian forms of the _Ornithoscelida_ (or _Dinosauria_ and
_Compsognatha_) have brought to light the existence of intercalary forms
between what have hitherto been always regarded as very distinct classes
of the vertebrate sub-kingdom, namely _Reptilia_ and _Aves_. Whatever
inferences may, or may not, be drawn from the fact, it is now an
established truth that, in many of these _Ornithoscelida_, the hind limbs
and the pelvis are much more similar to those of Birds than they are to
those of Reptiles, and that these Bird-reptiles, or Reptile-birds, were
more or less completely bipedal.

When I addressed you in 1862, I should have been bold indeed had I
suggested that palaeontology would before long show us the possibility of
a direct transition from the type of the lizard to that of the ostrich.
At the present moment, we have, in the _Ornithoscelida_, the intercalary
type, which proves that transition to be something more than a
possibility; but it is very doubtful whether any of the genera of
_Ornithoscelida_ with which we are at present acquainted are the actual
linear types by which the transition from the lizard to the bird was
effected. These, very probably, are still hidden from us in the older
formations.

Let us now endeavour to find some cases of true linear types, or forms
which are intermediate between others because they stand in a direct
genetic relation to them. It is no easy matter to find clear and
unmistakable evidence of filiation among fossil animals; for, in order
that such evidence should be quite satisfactory, it is necessary that we
should be acquainted with all the most important features of the
organisation of the animals which are supposed to be thus related, and
not merely with the fragments upon which the genera and species of the
palaeontologist are so often based. M. Gaudry has arranged the species of
_Hyoenidoe, Proboscidea, Rhinocerotidoe_, and _Equidoe_ in their order of
filiation from their earliest appearance in the Miocene epoch to the
present time, and Professor Ruetimeyer has drawn up similar schemes for
the Oxen and other _Ungulata_--with what, I am disposed to think, is a
fair and probable approximation to the order of nature. But, as no one is
better aware than these two learned, acute, and philosophical biologists,
all such arrangements must be regarded as provisional, except in those
cases in which, by a fortunate accident, large series of remains are
obtainable from a thick and widespread series of deposits. It is easy to
accumulate probabilities--hard to make out some particular case in such a
way that it will stand rigorous criticism.

After much search, however, I think that such a case is to be made out in
favour of the pedigree of the Horses.

The genus _Equus_ is represented as far back as the latter part of the
Miocene epoch; but in deposits belonging to the middle of that epoch its
place is taken by two other genera, _Hipparion_ and _Anchitherium_;[2]
and, in the lowest Miocene and upper Eocene, only the last genus occurs.
A species of _Anchitherium_ was referred by Cuvier to the _Paloeotheria_
under the name of _P. aurelianense_. The grinding-teeth are in fact very
similar in shape and in pattern, and in the absence of any thick layer of
cement, to those of some species of _Paloeotherium_, especially Cuvier's
_Paloeotherium minus_, which has been formed into a separate genus,
_Plagiolophus_, by Pomel. But in the fact that there are only six full-
sized grinders in the lower jaw, the first premolar being very small;
that the anterior grinders are as large as, or rather larger than, the
posterior ones; that the second premolar has an anterior prolongation;
and that the posterior molar of the lower jaw has, as Cuvier pointed out,
a posterior lobe of much smaller size and different form, the dentition
of _Anchitherium_ departs from the type of the _Paloeotherium_, and
approaches that of the Horse.

[Footnote 2: Hermann von Meyer gave the name of _Anchitherium_ to _A.
Ezquerroe_; and in his paper on the subject he takes great pains to
distinguish the latter as the type of a new genus, from Cuvier's
_Paloeotherium d'Orleans_. But it is precisely the _Paloeotherium
d'Orleans_ which is the type of Christol's genus _Hipparitherium_; and
thus, though _Hipparitherium_ is of later date than _Anchitherium_, it
seemed to me to have a sort of equitable right to recognition when this
Address was written. On the whole, however, it seems most convenient to
adopt _Anchitherium_.]

Again, the skeleton of _Anchitherium_ is extremely equine. M. Christol
goes so far as to say that the description of the bones of the horse, or
the ass, current in veterinary works, would fit those of _Anchitherium_.
And, in a general way, this may be true enough; but there are some most
important differences, which, indeed, are justly indicated by the same
careful observer. Thus the ulna is complete throughout, and its shaft is
not a mere rudiment, fused into one bone with the radius. There are three
toes, one large in the middle and one small on each side. The femur is
quite like that of a horse, and has the characteristic fossa above the
external condyle. In the British Museum there is a most instructive
specimen of the leg-bones, showing that the fibula was represented by the
external malleolus and by a flat tongue of bone, which extends up from it
on the outer side of the tibia, and is closely ankylosed with the latter
bone.[3] The hind toes are three, like those of the fore leg; and the
middle metatarsal bone is much less compressed from side to side than
that of the horse.

[Footnote 3: I am indebted to M. Gervais for a specimen which indicates
that the fibula was complete, at any rate, in some cases; and for a very
interesting ramps of a mandible, which shows that, as in the
_Paloeotheria_, the hindermost milk-molar of the lower jaw was devoid of
the posterior lobe which exists in the hindermost true molar.]

In the _Hipparion_, the teeth nearly resemble those of the Horses, though
the crowns of the grinders are not so long; like those of the Horses,
they are abundantly coated with cement. The shaft of the ulna is reduced
to a mere style, ankylosed throughout nearly its whole length with the
radius, and appearing to be little more than a ridge on the surface of
the latter bone until it is carefully examined. The front toes are still
three, but the outer ones are more slender than in _Anchitherium_, and
their hoofs smaller in proportion to that of the middle toe; they are, in
fact, reduced to mere dew-claws, and do not touch the ground. In the leg,
the distal end of the fibula is so completely united with the tibia that
it appears to be a mere process of the latter bone, as in the Horses.

In _Equus_, finally, the crowns of the grinding-teeth become longer, and
their patterns are slightly modified; the middle of the shaft of the ulna
usually vanishes, and its proximal and distal ends ankylose with the
radius. The phalanges of the two outer toes in each foot disappear, their
metacarpal and metatarsal bones being left as the "splints."

The _Hipparion_ has large depressions on the face in front of the orbits,
like those for the "larmiers" of many ruminants; but traces of these are
to be seen in some of the fossil horses from the Sewalik Hills; and, as
Leidy's recent researches show, they are preserved in _Anchitherium_.

When we consider these facts, and the further circumstance that the
Hipparions, the remains of which have been collected in immense numbers,
were subject, as M. Gaudry and others have pointed out, to a great range
of variation, it appears to me impossible to resist the conclusion that
the types of the _Anchitherium_, of the _Hipparion_, and of the ancient
Horses constitute the lineage of the modern Horses, the _Hipparion_ being
the intermediate stage between the other two, and answering to B in my
former illustration.

The process by which the _Anchitherium_ has been converted into _Equus_
is one of specialisation, or of more and more complete deviation from
what might be called the average form of an ungulate mammal. In the
Horses, the reduction of some parts of the limbs, together with the
special modification of those which are left, is carried to a greater
extent than in any other hoofed mammals. The reduction is less and the
specialisation is less in the _Hipparion_, and still less in the
_Anchitherium_; but yet, as compared with other mammals, the reduction
and specialisation of parts in the _Anchitherium_ remain great.

Is it not probable then, that, just as in the Miocene epoch, we find an
ancestral equine form less modified than _Equus_, so, if we go back to
the Eocene epoch, we shall find some quadruped related to the
_Anchitherium_, as _Hipparion_ is related to _Equus_, and consequently
departing less from the average form?

I think that this desideratum is very nearly, if not quite, supplied by
_Plagiolophus_, remains of which occur abundantly in some parts of the
Upper and Middle Eocene formations. The patterns of the grinding-teeth of
_Plagiolophus_ are similar to those of _Anchitherium_, and their crowns
are as thinly covered with cement; but the grinders diminish in size
forwards, and the last lower molar has a large hind lobe, convex outwards
and concave inwards, as in _Palueotherium_. The ulna is complete and much
larger than in any of the _Equidoe_, while it is more slender than in
most of the true _Paloeotheria_; it is fixedly united, but not ankylosed,
with the radius. There are three toes in the fore limb, the outer ones
being slender, but less attenuated than in the _Equidoe_. The femur is
more like that of the _Paloeotheria_ than that of the horse, and has only
a small depression above its outer condyle in the place of the great
fossa which is so obvious in the _Equidoe_. The fibula is distinct, but
very slender, and its distal end is ankylosed with the tibia. There are
three toes on the hind foot having similar proportions to those on the
fore foot. The principal metacarpal and metatarsal bones are flatter than
they are in any of the _Equidoe_; and the metacarpal bones are longer
than the metatarsals, as in the _Paloeotheria_.

In its general form, _Plagiolophus_ resembles a very small and slender
horse,[4] and is totally unlike the reluctant, pig-like creature depicted
in Cuvier's restoration of his _Paloeotherium minus_ in the "Ossemens
Fossiles."

[Footnote 4: Such, at least, is the conclusion suggested by the
proportions of the skeleton figured by Cuvier and De Blainville; but
perhaps something between a Horse and an Agouti would be nearest the
mark.]

It would be hazardous to say that _Plagiolophus_ is the exact radical
form of the Equine quadrupeds; but I do not think there can be any
reasonable doubt that the latter animals have resulted from the
modification of some quadruped similar to _Plagiolophus_.

We have thus arrived at the Middle Eocene formation, and yet have traced
back the Horses only to a three-toed stock; but these three-toed forms,
no less than the Equine quadrupeds themselves, present rudiments of the
two other toes which appertain to what I have termed the "average"
quadruped. If the expectation raised by the splints of the Horses that,
in some ancestor of the Horses, these splints would be found to be
complete digits, has been verified, we are furnished with very strong
reasons for looking for a no less complete verification of the
expectation that the three-toed _Plagiolophus_-like "avus" of the horse
must have had a five-toed "atavus" at some earlier period.

No such five-toed "atavus," however, has yet made its appearance among
the few middle and older Eocene _Mammalia_ which are known.

Another series of closely affiliated forms, though the evidence they
afford is perhaps less complete than that of the Equine series, is
presented to us by the _Dichobune_ of the Eocene epoch, the
_Cainotherium_ of the Miocene, and the _Tragulidoe_, or so-called "Musk-
deer," of the present day.

The _Tragulidoe_; have no incisors in the upper jaw, and only six
grinding-teeth on each side of each jaw; while the canine is moved up to
the outer incisor, and there is a diastema in the lower jaw. There are
four complete toes on the hind foot, but the middle metatarsals usually
become, sooner or later, ankylosed into a cannon bone. The navicular and
the cuboid unite, and the distal end of the fibula is ankylosed with the
tibia.

In _Cainotherium_ and _Dichobune_ the upper incisors are fully developed.
There are seven grinders; the teeth form a continuous series without a
diastema. The metatarsals, the navicular and cuboid, and the distal end
of the fibula, remain free. In the _Cainotherium_, also, the second
metacarpal is developed, but is much shorter than the third, while the
fifth is absent or rudimentary. In this respect it resembles
_Anoplotherium secundarium_. This circumstance, and the peculiar pattern
of the upper molars in _Cainotherium_, lead me to hesitate in considering
it as the actual ancestor of the modern _Tragulidoe_. If _Dichobune_ has
a fore-toed fore foot (though I am inclined to suspect that it resembles
_Cainotherium_), it will be a better representative of the oldest forms
of the Traguline series; but _Dichobune_ occurs in the Middle Eocene, and
is, in fact, the oldest known artiodactyle mammal. Where, then, must we
look for its five-toed ancestor?

If we follow down other lines of recent and tertiary _Ungulata_, the same
question presents itself. The Pigs are traceable back through the Miocene
epoch to the Upper Eocene, where they appear in the two well-marked forms
of _Hyopopotamus_ and _Choeropotamus_; but _Hyopotamus_ appears to have
had only two toes.

Again, all the great groups of the Ruminants, the _Bovidoe, Antilopidoe,
Camelopardalidoe_, and _Cervidoe_, are represented in the Miocene epoch,
and so are the Camels. The Upper Eocene _Anoplotherium_, which is
intercalary between the Pigs and the _Tragulidoe_, has only two, or, at
most, three toes. Among the scanty mammals of the Lower Eocene formation
we have the perissodactyle _Ungulata_ represented by _Coryphodon,
Hyracotherium_, and _Pliolophus_. Suppose for a moment, for the sake of
following out the argument, that _Pliolophus_ represents the primary
stock of the Perissodactyles, and _Dichobune_ that of the Artiodactyles
(though I am far from saying that such is the case), then we find, in the
earliest fauna of the Eocene epoch to which our investigations carry us,
the two divisions of the _Ungulata_ completely differentiated, and no
trace of any common stock of both, or of five-toed predecessors to
either. With the case of the Horses before us, justifying a belief in the
production of new animal forms by modification of old ones, I see no
escape from the necessity of seeking for these ancestors of the
_Ungulata_ beyond the limits of the Tertiary formations.

I could as soon admit special creation, at once, as suppose that the
Perissodactyles and Artiodactyles had no five-toed ancestors. And when we
consider how large a portion of the Tertiary period elapsed before
_Anchitherium_ was converted into _Equus_, it is difficult to escape the
conclusion that a large proportion of time anterior to the Tertiary
period must have been expended in converting the common stock of the
_Ungulata_ into Perissodactyles and Artiodactyles.

The same moral is inculcated by the study of every other order of
Tertiary monodelphous _Mammalia_. Each of these orders is represented in
the Miocene epoch: the Eocene formation, as I have already said, contains
_Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora_, and _Cetacea_.
But the _Cheiroptera_ are extreme modifications of the _Insectivora_,
just as the _Cetacea_ are extreme modifications of the Carnivorous type;
and therefore it is to my mind incredible that monodelphous _Insectivora_
and _Carnivora_ should not have been abundantly developed, along with
_Ungulata_, in the Mesozoic epoch. But if this be the case, how much
further back must we go to find the common stock of the monodelphous
_Mammalia_? As to the _Didelphia_, if we may trust the evidence which
seems to be afforded by their very scanty remains, a Hypsiprymnoid form
existed at the epoch of the Trias, contemporaneously with a Carnivorous
form. At the epoch of the Trias, therefore, the _Marsupialia_ must have
already existed long enough to have become differentiated into
carnivorous and herbivorous forms. But the _Monotremata_ are lower forms
than the _Didelphia_ which last are intercalary between the
_Ornithodelphia_ and the _Monodelphia_. To what point of the Palaeozoic
epoch, then, must we, upon any rational estimate, relegate the origin of
the _Monotremata?_

The investigation of the occurrence of the classes and of the orders of
the _Sauropsida_ in time points in exactly the same direction. If, as
there is great reason to believe, true Birds existed in the Triassic
epoch, the ornithoscelidous forms by which Reptiles passed into Birds
must have preceded them. In fact there is, even at present, considerable
ground for suspecting the existence of _Dinosauria_ in the Permian
formations; but, in that case, lizards must be of still earlier date. And
if the very small differences which are observable between the
_Crocodilia_ of the older Mesozoic formations and those of the present
day furnish any sort of approximation towards an estimate of the average
rate of change among the _Sauropsida_, it is almost appalling to reflect
how far back in Palaeozoic times we must go, before we can hope to arrive
at that common stock from which the _Crocodilia, Lacertilia,
Ornithoscelida_, and _Plesiosauria_, which had attained so great a
development in the Triassic epoch, must have been derived.

The _Amphibia_ and _Pisces_ tell the same story. There is not a single
class of vertebrated animals which, when it first appears, is represented
by analogues of the lowest known members of the same class. Therefore, if
there is any truth in the doctrine of evolution, every class must be
vastly older than the first record of its appearance upon the surface of
the globe. But if considerations of this kind compel us to place the
origin of vertebrated animals at a period sufficiently distant from the
Upper Silurian, in which the first Elasmobranchs and Ganoids occur, to
allow of the evolution of such fishes as these from a Vertebrate as
simple as the _Amphioxus,_ I can only repeat that it is appalling to
speculate upon the extent to which that origin must have preceded the
epoch of the first recorded appearance of vertebrate life.


Such is the further commentary which I have to offer upon the statement
of the chief results of palaeontology which I formerly ventured to lay
before you.

But the growth of knowledge in the interval makes me conscious of an
omission of considerable moment in that statement, inasmuch as it
contains no reference to the bearings of palaeontology upon the theory of
the distribution of life; nor takes note of the remarkable manner in
which the facts of distribution, in present and past times, accord with
the doctrine of evolution, especially in regard to land animals.

That connection between palaeontology and geology and the present
distribution of terrestrial animals, which so strikingly impressed Mr.
Darwin, thirty years ago, as to lead him to speak of a "law of succession
of types," and of the wonderful relationship on the same continent
between the dead and the living, has recently received much elucidation
from the researches of Gaudry, of Rutimeyer, of Leidy, and of Alphonse
Milne-Edwards, taken in connection with the earlier labours of our
lamented colleague Falconer; and it has been instructively discussed in
the thoughtful and ingenious work of Mr. Andrew Murray "On the
Geographical Distribution of Mammals."[5]

[Footnote 5: The paper "On the Form and Distribution of the Landtracts
during the Secondary and Tertiary Periods respectively; and on the Effect
upon Animal Life which great Changes in Geographical Configuration have
probably produced," by Mr. Searles V. Wood, jun., which was published in
the _Philosophical Magazine_, in 1862, was unknown to me when this
Address was written. It is well worthy of the most careful study.]

I propose to lay before you, as briefly as I can, the ideas to which a
long consideration of the subject has given rise in my mind.

If the doctrine of evolution is sound, one of its immediate consequences
clearly is, that the present distribution of life upon the globe is the
product of two factors, the one being the distribution which obtained in
the immediately preceding epoch, and the other the character and the
extent of the changes which have taken place in physical geography
between the one epoch and the other; or, to put the matter in another
way, the Fauna and Flora of any given area, in any given epoch, can
consist only of such forms of life as are directly descended from those
which constituted the Fauna and Flora of the same area in the immediately
preceding epoch, unless the physical geography (under which I include
climatal conditions) of the area has been so altered as to give rise to
immigration of living forms from some other area.

The evolutionist, therefore, is bound to grapple with the following
problem whenever it is clearly put before him:--Here are the Faunae of the
same area during successive epochs. Show good cause for believing either
that these Faunae have been derived from one another by gradual
modification, or that the Faunae have reached the area in question by
migration from some area in which they have undergone their development.

I propose to attempt to deal with this problem, so far as it is
exemplified by the distribution of the terrestrial _Vertebrata_, and I
shall endeavour to show you that it is capable of solution in a sense
entirely favourable to the doctrine of evolution.

I have elsewhere[6] stated at length the reasons which lead me to
recognise four primary distributional provinces for the terrestrial
_Vertebrata_ in the present world, namely,--first, the _Novozelanian_, or
New-Zealand province; secondly, the _Australian_ province, including
Australia, Tasmania, and the Negrito Islands; thirdly, _Austro-Columbia_,
or South America _plus_ North America as far as Mexico; and fourthly, the
rest of the world, or _Arctogoea_, in which province America north of
Mexico constitutes one sub-province, Africa south of the Sahara a second,
Hindostan a third, and the remainder of the Old World a fourth.

[Footnote 6: "On the Classification and Distribution of the
Alectoromorphoe;" _Proceedings of the Zoological Society_, 1868.]

Now the truth which Mr. Darwin perceived and promulgated as "the law of
the succession of types" is, that, in all these provinces, the animals
found in Pliocene or later deposits are closely affined to those which
now inhabit the same provinces; and that, conversely, the forms
characteristic of other provinces are absent. North and South America,
perhaps, present one or two exceptions to the last rule, but they are
readily susceptible of explanation. Thus, in Australia, the later
Tertiary mammals are marsupials (possibly with the exception of the Dog
and a Rodent or two, as at present). In Austro-Columbia, the later
Tertiary fauna exhibits numerous and varied forms of Platyrrhine Apes,
Rodents, Cats, Dogs, Stags, _Edentata_, and Opossums; but, as at present,
no Catarrhine Apes, no Lemurs, no _Insectivora_, Oxen, Antelopes,
Rhinoceroses, nor _Didelphia_ other than Opossums. And in the widespread
Arctogaeal province, the Pliocene and later mammals belong to the same
groups as those which now exist in the province. The law of succession of
types, therefore, holds good for the present epoch as compared with its
predecessor. Does it equally well apply to the Pliocene fauna when we
compare it with that of the Miocene epoch? By great good fortune, an
extensive mammalian fauna of the latter epoch has now become known, in
four very distant portions of the Arctogaeal province which do not differ
greatly in latitude. Thus Falconer and Cautley have made known the fauna
of the sub-Himalayas and the Perim Islands; Gaudry that of Attica; many
observers that of Central Europe and France; and Leidy that of Nebraska,
on the eastern flank of the Rocky Mountains. The results are very
striking. The total Miocene fauna comprises many genera and species of
Catarrhine Apes, of Bats, of _Insectivora_; of Arctogaeal types of
_Rodentia_; of _Proboscidea_; of equine, rhinocerotic, and tapirine
quadrupeds; of cameline, bovine, antilopine, cervine, and traguline
Ruminants; of Pigs and Hippopotamuses; of _Viverridoe_ and _Hyoenidoe_
among other _Carnivora_; with _Edentata_ allied to the Aretogaeal
_Oryeteropus_ and _Manis_, and not to the Austro-Columbian Edentates. The
only type present in the Miocene, but absent in the existing, fauna of
Eastern Arctogaea, is that of the _Didelphidoe_, which, however, remains
in North America.

But it is very remarkable that while the Miocene fauna of the Arctogaeal
province, as a whole, is of the same character as the existing fauna of
the same province, as a whole, the component elements of the fauna were
differently associated. In the Miocene epoch, North America possessed
Elephants, Horses, Rhinoceroses, and a great number and variety of
Ruminants and Pigs, which are absent in the present indigenous fauna;
Europe had its Apes, Elephants, Rhinoceroses, Tapirs, Musk-deer,
Giraffes, Hyaenas, great Cats, Edentates, and Opossum-like Marsupials,
which have equally vanished from its present fauna; and in Northern
India, the African types of Hippopotamuses, Giraffes, and Elephants were
mixed up with what are now the Asiatic types of the latter, and with
Camels, and Semnopithecine and Pithecine Apes of no less distinctly
Asiatic forms.

In fact the Miocene mammalian fauna of Europe and the Himalayan regions
contains, associated together, the types which are at present separately
located in the South-African and Indian sub-provinces of Arctogaea. Now
there is every reason to believe, on other grounds, that both Hindostan,
south of the Ganges, and Africa, south of the Sahara, were separated by a
wide sea from Europe and North Asia during the Middle and Upper Eocene
epochs. Hence it becomes highly probable that the well-known
similarities, and no less remarkable differences between the present
Faunae of India and South Africa have arisen in some such fashion as the
following. Some time during the Miocene epoch, possibly when the
Himalayan chain was elevated, the bottom of the nummulitic sea was
upheaved and converted into dry land, in the direction of a line
extending from Abyssinia to the mouth of the Ganges. By this means, the
Dekhan on the one hand, and South Africa on the other, became connected
with the Miocene dry land and with one another. The Miocene mammals
spread gradually over this intermediate dry land; and if the condition of
its eastern and western ends offered as wide contrasts as the valleys of
the Ganges and Arabia do now, many forms which made their way into Africa
must have been different from those which reached the Dekhan, while
others might pass into both these sub-provinces.

That there was a continuity of dry land between Europe and North America
during the Miocene epoch, appears to me to be a necessary consequence of
the fact that many genera of terrestrial mammals, such as _Castor,
Hystrix, Elephas, Mastodon, Equus, Hipparion, Anchitherium, Rhinoceros,
Cervus, Amphicyon, Hyoenarctos_, and _Machairodus_, are common to the
Miocene formations of the two areas, and have as yet been found (except
perhaps _Anchitherium_) in no deposit of earlier age. Whether this
connection took place by the east, or by the west, or by both sides of
the Old World, there is at present no certain evidence, and the question
is immaterial to the present argument; but, as there are good grounds for
the belief that the Australian province and the Indian and South-African
sub-provinces were separated by sea from the rest of Arctogaea before the
Miocene epoch, so it has been rendered no less probable, by the
investigations of Mr. Carrick Moore and Professor Duncan, that Austro-
Columbia was separated by sea from North America during a large part of
the Miocene epoch.

It is unfortunate that we have no knowledge of the Miocene mammalian
fauna of the Australian and Austro-Columbian provinces; but, seeing that
not a trace of a Platyrrhine Ape, of a Procyonine Carnivore, of a
characteristically South-American Rodent, of a Sloth, an Armadillo, or an
Ant-eater has yet been found in Miocene deposits of Arctogaea, I cannot
doubt that they already existed in the Miocene Austro-Columbian province.

Nor is it less probable that the characteristic types of Australian
Mammalia were already developed in that region in Miocene times.

But Austro-Columbia presents difficulties from which Australia is free;
_Cantelidoe_ and _Tapirdoe_ are now indigenous in South America as they
are in Arctogaea; and, among the Pliocene Austro-Columbian mammals, the
Arctogaeal genera _Equus, Mastodon,_ and _Machairodus_ are numbered. Are
these Postmiocene immigrants, or Praemiocene natives?

Still more perplexing are the strange and interesting forms _Toxodon,
Macrauchenia, Typotherium_, and a new Anoplotherioid mammal
(_Homalodotherhon_) which Dr. Cunningham sent over to me some time ago
from Patagonia. I confess I am strongly inclined to surmise that these
last, at any rate, are remnants of the population of Austro-Columbia
before the Miocene epoch, and were not derived from Arctogaea by way of
the north and east.

The fact that this immense fauna of Miocene Arctogaea is now fully and
richly represented only in India and in South Africa, while it is shrunk
and depauperised in North Asia, Europe, and North America, becomes at
once intelligible, if we suppose that India and South Africa had but a
scanty mammalian population before the Miocene immigration, while the
conditions were highly favourable to the new comers. It is to be supposed
that these new regions offered themselves to the Miocene Ungulates, as
South America and Australia offered themselves to the cattle, sheep, and
horses of modern colonists. But, after these great areas were thus
peopled, came the Glacial epoch, during which the excessive cold, to say
nothing of depression and ice-covering, must have almost depopulated all
the northern parts of Arctogaea, destroying all the higher mammalian
forms, except those which, like the Elephant and Rhinoceros, could adjust
their coats to the altered conditions. Even these must have been driven
away from the greater part of the area; only those Miocene mammals which
had passed into Hindostan and into South Africa would escape decimation
by such changes in the physical geography of Arctogaea. And when the
northern hemisphere passed into its present condition, these lost tribes
of the Miocene Fauna were hemmed by the Himalayas, the Sahara, the Red
Sea, and the Arabian deserts, within their present boundaries.

Now, on the hypothesis of evolution, there is no sort of difficulty in
admitting that the differences between the Miocene forms of the mammalian
Fauna and those which exist at present are the results of gradual
modification; and, since such differences in distribution as obtain are
readily explained by the changes which have taken place in the physical
geography of the world since the Miocene epoch, it is clear that the
result of the comparison of the Miocene and present Faunae is distinctly
in favour of evolution. Indeed I may go further. I may say that the
hypothesis of evolution explains the facts of Miocene, Pliocene, and
Recent distribution, and that no other supposition even pretends to
account for them. It is, indeed, a conceivable supposition that every
species of Rhinoceros and every species of Hyaena, in the long succession
of forms between the Miocene and the present species, was separately
constructed out of dust, or out of nothing, by supernatural power; but
until I receive distinct evidence of the fact, I refuse to run the risk
of insulting any sane man by supposing that he seriously holds such a
notion.

Let us now take a step further back in time, and inquire into the
relations between the Miocene Fauna and its predecessor of the Upper
Eocene formation.

Here it is to be regretted that our materials for forming a judgment are
nothing to be compared in point of extent or variety with those which are
yielded by the Miocene strata. However, what we do know of this Upper
Eocene Fauna of Europe gives sufficient positive information to enable us
to draw some tolerably safe inferences. It has yielded representatives of
_Insectivora_, of _Cheiroptera_, of _Rodentia_, of _Carnivora_, of
artiodactyle and perissodactyle _Ungulata_, and of opossum-like
Marsupials. No Australian type of Marsupial has been discovered in the
Upper Eocene strata, nor any Edentate mammal. The genera (except perhaps
in the case of some of the _Insectivora, Cheiroptera_, and _Rodentia_)
are different from those of the Miocene epoch, but present a remarkable
general similarity to the Miocene and recent genera. In several cases, as
I have already shown, it has now been clearly made out that the relation
between the Eocene and Miocene forms is such that the Eocene form is the
less specialised; while its Miocene ally is more so, and the
specialisation reaches its maximum in the recent forms of the same type.

So far as the Upper Eocene and the Miocene Mammalian Faunae are
comparable, their relations are such as in no way to oppose the
hypothesis that the older are the progenitors of the more recent forms,
while, in some cases, they distinctly favour that hypothesis. The period
in tine and the changes in physical geography represented by the
nummulitic deposits are undoubtedly very great, while the remains of
Middle Eocene and Older Eocene Mammals are comparatively few. The general
facies of the Middle Eocene Fauna, however, is quite that of the Upper.
The Older Eocene pre-nummulitic mammalian Fauna contains Bats, two genera
of _Carivora_, three genera of _Ungulata_ (probably all perissodactyle),
and a didelphid Marsupial; all these forms, except perhaps the Bat and
the Opossum, belong to genera which are not known to occur out of the
Lower Eocene formation. The _Coryphodon_ appears to have been allied to
the Miocene and later Tapirs, while _Pliolophus_, in its skull and
dentition, curiously partakes of both artiodactyle and perissodactyle
characters; the third trochanter upon its femur, and its three-toed hind
foot, however, appear definitely to fix its position in the latter
division.

There is nothing, then, in what is known of the older Eocene mammals of
the Arctogaeal province to forbid the supposition that they stood in an
ancestral relation to those of the Calcaire Grossier and the Gypsum of
the Paris basin, and that our present fauna, therefore, is directly
derived from that which already existed in Arctogaea at the commencement
of the Tertiary period. But if we now cross the frontier between the
Cainozoic and the Mesozoic faunae, as they are preserved within the
Arctogaeal area, we meet with an astounding change, and what appears to be
a complete and unmistakable break in the line of biological continuity.

Among the twelve or fourteen species of _Mammalia_ which are said to have
been found in the Purbecks, not one is a member of the orders
_Cheiroptera, Rodentia, Ungulata_, or _Carnivora_, which are so well
represented in the Tertiaries. No _Insectivora_ are certainly known, nor
any opossum-like Marsupials. Thus there is a vast negative difference
between the Cainozoic and the Mesozoic mammalian faunae of Europe. But
there is a still more important positive difference, inasmuch as all
these Mammalia appear to be Marsupials belonging to Australian groups,
and thus appertaining to a different distributional province from the
Eocene and Miocene marsupials, which are Austro-Columbian. So far as the
imperfect materials which exist enable a judgment to be formed, the same
law appears to have held good for all the earlier Mesozoic _Mammalia_. Of
the Stonesfield slate mammals, one, _Amphitherium_, has a definitely
Australian character; one, _Phascolotherium_, may be either Dasyurid or
Didelphine; of a third, _Stereognathus_, nothing can at present be said.
The two mammals of the Trias, also, appear to belong to Australian
groups.

Every one is aware of the many curious points of resemblance between the
marine fauna of the European Mesozoic rocks and that which now exists in
Australia. But if there was this Australian facies about both the
terrestrial and the marine faunae of Mesozoic Europe, and if there is this
unaccountable and immense break between the fauna of Mesozoic and that of
Tertiary Europe, is it not a very obvious suggestion that, in the
Mesozoic epoch, the Australian province included Europe, and that the
Arctogaeal province was contained within other limits? The Arctogaeal
province is at present enormous, while the Australian is relatively
small. Why should not these proportions have been different during the
Mesozoic epoch?

Thus I am led to think that by far the simplest and most rational mode of
accounting for the great change which took place in the living
inhabitants of the European area at the end of the Mesozoic epoch, is the
supposition that it arose from a vast alteration of the physical
geography of the globe; whereby an area long tenanted by Cainozoic forms
was brought into such relations with the European area that migration
from the one to the other became possible, and took place on a great
scale.

This supposition relieves us, at once, from the difficulty in which we
were left, some time ago, by the arguments which I used to demonstrate
the necessity of the existence of all the great types of the Eocene epoch
in some antecedent period.

It is this Mesozoic continent (which may well have lain in the
neighbourhood of what are now the shores of the North Pacific Ocean)
which I suppose to have been occupied by the Mesozoic _Monodelphia_; and
it is in this region that I conceive they must have gone through the long
series of changes by which they were specialised into the forms which we
refer to different orders. I think it very probable that what is now
South America may have received the characteristic elements of its
mammalian fauna during the Mesozoic epoch; and there can be little doubt
that the general nature of the change which took place at the end of the
Mesozoic epoch in Europe was the upheaval of the eastern and northern
regions of the Mesozoic sea-bottom into a westward extension of the
Mesozoic continent, over which the mammalian fauna, by which it was
already peopled, gradually spread. This invasion of the land was prefaced
by a previous invasion of the Cretaceous sea by modern forms of mollusca
and fish.

It is easy to imagine how an analogous change might come about in the
existing world. There is, at present, a great difference between the
fauna of the Polynesian Islands and that of the west coast of America.
The animals which are leaving their spoils in the deposits now forming in
these localities are widely different. Hence, if a gradual shifting of
the deep sea, which at present bars migration between the easternmost of
these islands and America, took place to the westward, while the American
side of the sea-bottom was gradually upheaved, the palaeontologist of the
future would find, over the Pacific area, exactly such a change as I am
supposing to have occurred in the North-Atlantic area at the close of the
Mesozoic period. An Australian fauna would be found underlying an
American fauna, and the transition from the one to the other would be as
abrupt as that between the Chalk and lower Tertiaries; and as the
drainage-area of the newly formed extension of the American continent
gave rise to rivers and lakes, the mammals mired in their mud would
differ from those of like deposits on the Australian side, just as the
Eocene mammals differ from those of the Purbecks.

How do similar reasonings apply to the other great change of life--that
which took place at the end of the Palaeozoic period?

In the Triassic epoch, the distribution of the dry land and of
terrestrial vertebrate life appears to have been, generally, similar to
that which existed in the Mesozoic epoch; so that the Triassic continents
and their faunae seem to be related to the Mesozoic lands and their faunae,
just as those of the Miocene epoch are related to those of the present
day. In fact, as I have recently endeavoured to prove to the Society,
there was an Arctogaeal continent and an Arctogaeal province of
distribution in Triassic times as there is now; and the _Sauropsida_ and
_Marsupialia_ which constituted that fauna were, I doubt not, the
progenitors of the _Sauropsida_ and _Marsupialia_ of the whole Mesozoic
epoch.

Looking at the present terrestrial fauna of Australia, it appears to me
to be very probable that it is essentially a remnant of the fauna of the
Triassic, or even of an earlier, age[7] in which case Australia must at
that time have been in continuity with the Arctogaeal continent.

[Footnote 7: Since this Address was read, Mr. Krefft has sent us news of
the discovery in Australia of a freshwater fish of strangely Palaeozoic
aspect, and apparently a Ganoid intermediate between _Dipterus_ and
_Lepidosiren_. [The now well-known _Ceratodus_. 1894.]]

But now comes the further inquiry, Where was the highly differentiated
Sauropsidan fauna of the Trias in Palaeozoic times? The supposition that
the Dinosaurian, Crocodilian, Dicynodontian, and to Plesiosaurian types
were suddenly created at the end of the Permian epoch may be dismissed,
without further consideration, as a monstrous and unwarranted assumption.
The supposition that all these types were rapidly differentiated out of
_Lacertilia_ in the time represented by the passage from the Palaeozoic to
the Mesozoic formation, appears to me to be hardly more credible, to say
nothing of the indications of the existence of Dinosaurian forms in the
Permian rocks which have already been obtained.

For my part, I entertain no sort of doubt that the Reptiles, Birds, and
Mammals of the Trias are the direct descendants of Reptiles, Birds, and
Mammals which existed in the latter part of the Palaeozoic epoch, but not
in any area of the present dry land which has yet been explored by the
geologist.

This may seem a bold assumption, but it will not appear unwarrantable to
those who reflect upon the very small extent of the earth's surface which
has hitherto exhibited the remains of the great Mammalian fauna of the
Eocene times. In this respect, the Permian land Vertebrate fauna appears
to me to be related to the Triassic much as the Eocene is to the Miocene.
Terrestrial reptiles have been found in Permian rocks only in three
localities; in some spots of France, and recently of England, and over a
more extensive area in Germany. Who can suppose that the few fossils yet
found in these regions give any sufficient representation of the Permian
fauna?

It may be said that the Carboniferous formations demonstrate the
existence of a vast extent of dry land in the present dry-land area, and
that the supposed terrestrial Palaeozoic Vertebrate Fauna ought to have
left its remains in the Coal-measures, especially as there is now reason
to believe that much of the coal was formed by the accumulation of spores
and sporangia on dry land. But if we consider the matter more closely, I
think that this apparent objection loses its force. It is clear that,
during the Carboniferous epoch, the vast area of land which is now
covered by Coal-measures must have been undergoing a gradual depression.
The dry land thus depressed must, therefore, have existed, as such,
before the Carboniferous epoch--in other words, in Devonian times--and
its terrestrial population may never have been other than such as existed
during the Devonian, or some previous epoch, although much higher forms
may have been developed elsewhere.

Again, let me say that I am making no gratuitous assumption of
inconceivable changes. It is clear that the enormous area of Polynesia
is, on the whole, an area over which depression has taken place to an
immense extent; consequently a great continent, or assemblage of
subcontinental masses of land must have existed at some former time, and
that at a recent period, geologically speaking, in the area of the
Pacific. But if that continent had contained Mammals, some of them must
have remained to tell the tale; and as it is well known that these
islands have no indigenous _Mammalia_, it is safe to assume that none
existed. Thus, midway between Australia and South America, each of which
possesses an abundant and diversified mammalian fauna, a mass of land,
which may have been as large as both put together, must have existed
without a mammalian inhabitant. Suppose that the shores of this great
land were fringed, as those of tropical Australia are now, with belts of
mangroves, which would extend landwards on the one side, and be buried
beneath littoral deposits on the other side, as depression went on; and
great beds of mangrove lignite might accumulate over the sinking land.
Let upheaval of the whole now take place, in such a manner as to bring
the emerging land into continuity with the South-American or Australian
continent, and, in course of time, it would be peopled by an extension of
the fauna of one of these two regions--just as I imagine the European
Permian dry land to have been peopled.

I see nothing whatever against the supposition that distributional
provinces of terrestrial life existed in the Devonian epoch, inasmuch as
M. Barrande has proved that they existed much earlier. I am aware of no
reason for doubting that, as regards the grades of terrestrial life
contained in them, one of these may have been related to another as New
Zealand is to Australia, or as Australia is to India, at the present day.
Analogy seems to me to be rather in favour of, than against, the
supposition that while only Ganoid fishes inhabited the fresh waters of
our Devonian land, _Amphibia_ and _Reptilia_, or even higher forms, may
have existed, though we have not yet found them. The earliest
Carboniferous _Amphibia_ now known, such as _Anthracosaurus_, are so
highly specialised that I can by no means conceive that they have been
developed out of piscine forms in the interval between the Devonian and
the Carboniferous periods, considerable as that is. And I take refuge in
one of two alternatives: either they existed in our own area during the
Devonian epoch and we have simply not yet found them; or they formed part
of the population of some other distributional province of that day, and
only entered our area by migration at the end of the Devonian epoch.
Whether _Reptilia_ and _Mammalia_ existed along with them is to me, at
present, a perfectly open question, which is just as likely to receive an
affirmative as a negative answer from future inquirers.

Let me now gather together the threads of my argumentation into the form
of a connected hypothetical view of the manner in which the distribution
of living and extinct animals has been brought about.

I conceive that distinct provinces of the distribution of terrestrial
life have existed since the earliest period at which that life is
recorded, and possibly much earlier; and I suppose, with Mr. Darwin, that
the progress of modification of terrestrial forms is more rapid in areas
of elevation than in areas of depression. I take it to be certain that
Labyrinthodont _Amphibia_ existed in the distributional province which
included the dry land depressed during the Carboniferous epoch; and I
conceive that, in some other distributional provinces of that day, which
remained in the condition of stationary or of increasing dry land, the
various types of the terrestrial _Sauropsida_ and of the _Mammalia_ were
gradually developing.

The Permian epoch marks the commencement of a new movement of upheaval in
our area, which dry land existed in North America, Europe, Asia, and
Africa, as it does now. Into this great new continental area the Mammals,
Birds, and Reptiles developed during the Palaeozoic epoch spread, and
formed the great Triassic Arctogaeal province. But, at the end of the
Triassic period, the movement of depression recommenced in our area,
though it was doubtless balanced by elevation elsewhere; modification and
development, checked in the one province, went on in that "elsewhere";
and the chief forms of Mammals, Birds and Reptiles, as we know them, were
evolved and peopled the Mesozoic continent. I conceive Australia to have
become separated from the continent as early as the end of the Triassic
epoch, or not much later. The Mesozoic continent must, I conceive, have
lain to the east, about the shores of the North Pacific and Indian
Oceans; and I am inclined to believe that it continued along the eastern
side of the Pacific area to what is now the province of Austro-Columbia,
the characteristic fauna of which is probably a remnant of the population
of the latter part of this period.

Towards the latter part of the Mesozoic period the movement of upheaval
around the shores of the Atlantic once more recommenced, and was very
probably accompanied by a depression around those of the Pacific. The
Vertebrate fauna elaborated in the Mesozoic continent moved westward and
took possession of the new lands, which gradually increased in extent up
to, and in some directions after, the Miocene epoch.

It is in favour of this hypothesis, I think, that it is consistent with
the persistence of a general uniformity in the positions of the great
masses of land and water. From the Devonian period, or earlier, to the
present day, the four great oceans, Atlantic, Pacific, Arctic, and
Antarctic, may have occupied their present positions, and only their
coasts and channels of communication have undergone an incessant
alteration. And, finally, the hypothesis I have put before you requires
no supposition that the rate of change in organic life has been either
greater or less in ancient times than it is now; nor any assumption,
either physical or biological, which has not its justification in
analogous phenomena of existing nature.

I have now only to discharge the last duty of my office, which is to
thank you, not only for the patient attention with which you have
listened to me so long to-day, but also for the uniform kindness with
which, for the past two years, you have rendered my endeavours to perform
the important, and often laborious, functions of your President a
pleasure instead of a burden.





End of the Project Gutenberg EBook of Discourses, by Thomas H. Huxley

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