» For the alien race in Stephen Donaldson's The Gap Cycle, see Amnion (Gap Cycle). The amnion is a membranous sac that surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota”; but not in amphibian and fish, which are consequently termed “Anamnia”. The primary function of this is the protection of the embryo for its future development into a fetus and eventually an animal. In humans In the human embryo the e… (More on Amnion)