Chapter 20 Flashcards: History of the Vertebrates
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a rigid but flexible structure that all chordate animals possess
notochord
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the membrane that provides a watertight fluid-filled environment for the embryo in a reptile egg
amnion
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mammals that lay eggs, such as the Echidna
monotremes
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an organ that evolved from membranes in the amniotic egg and allows the embryo to receive nutrients from the mother
placenta