Embryology Interview Question:

Are the extra embryonic membranes the same in all vertebrates?

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The presence of each extra embryonic membrane varies according to the vertebrate class.

In fishes and amphibians, only the yolk sac is present. In reptiles and aves besides the yolk sac, there are also the amnion, the chorion and the allantois. In placental mammals besides all these membranes, the placenta is present too.
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