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Do every mammal have placenta

Do every mammal have placenta?

E

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Mammals of monotreme group (echidnas, platypus) are oviparous, egg-laying, and they don’t have a placenta. Mammals of marsupial group (koalas, kangaroos, opossums) don’t encompass a placenta either; females of this set give birth to embryonic young that then keep on development in the mother’s pouch. Placenta only forms in the female placental mammals.

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