Amniotic  egg  of  a  bird and
   other reptiles.
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   The allantois holds metabolic wastes produced by the embryo.
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   The  chorion  and  the allantois exchange gases between the embryo and
   the air.
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   The  amnion protects the embryo in a fluid-filled cavity that cushions
   against mechanical shock.
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   The yolk sac provides nutrients via blood vessels; other nutrients are
   stored in the albumen (egg white).