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