Section 35. the Early Development of the Rabbit Is Apt to Puzzle

students a little at first. We have an ovum practically free from yolk (alecithal), and, therefore, we find it dividing completely and almost equally. We naturally assume, from what we have learnt, that the next stages will be the formation of a hollow blastosphere, invagination, a gastrula forming mesoblast by hollow outgrowths from the archenteron, and so on. There is no yolk here to substitute epiboly (Section 9) for invagination, nor to obliterate the archenteron and the blastopore through its pressure.

Yet none of these things we have anticipated occur!

We find solid mesoblastic somites, we find primitive streak, allantois and amnion, features we have just been explaining as the consequence of an excess of yolk in the egg. We even find a yolk sac with no yolk in it.