| A critical evolutionary development for terrestrial animals is the reptilian amniotic egg, now also characteristic of birds and some mammals. The developing embryo, protected from drying out, can survive outside of water and in a variety of habitats. The yolk provides it with food, and the albumin supplies water and nutrients. Wastes are released to the allantois, an extension of the embryonic gut. Oxygen diffuses easily through the thin outer shell of the egg; its passage to the embryo is regulated by the chorion. |
Hotmail
