The amniotic egg
contains several membranes that allowed animals to live a fully terrestrial life style.
- The amnion
protects the embryo in a fluid-filled cavity that serves as a cushion.
- The allantois holds metabolic wastes produced by the embryo.
- The chorion exchanges gases between the embryo and the air.
- The yolk sac
provides nutrients; other nutrients are stored in the albumen (egg white).