Reptile Traits: the Amniotic Egg
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Reptiles lay an amniotic egg, whose internal membranes and shell let the embryo develop away from standing water, unlike amphibians.
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A turtle's leathery-shelled egg retains moisture and exchanges gas through its shell while developing on dry land.
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Students often assume the shell seals the embryo off entirely — it must stay gas-permeable for oxygen and carbon dioxide exchange.