taxon constraints, yolk sacs and extraembryonic membranes

[cmungall]

1. EE membranes are only found in amniotes (Kardong)
2. yolk sacs are found across vertebrates (Kardong, various), and are homologous (Bgee, via Kardong)
3. yolk sacs are the primary anamniote EE membrane (Lombardi, comparative vertebrate reproduction)

This leads to TCVs.

One solution would be to subclass YS into the various different types, but this could lead to term inflation

Another solution is to make axiom 3 an Evo-GCI, but this is complicated and odd (although it would be useful to capture other variabilities about the yolk sac using Evo-GCIs.

The simplest solution for now is to remove axiom 1, and push down the TCs to the other 3 EEMs