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1 A membrane enclosing the embryo, yolk sac, and allantois of reptiles, birds, and mammals. In mammals a section of the chorion becomes the embryonic part of the placenta. See extraembryonic membranes.

2 The protective shell of an insect egg, produced by the ovary. It is pierced by a small pore (micropyle) that allows the entry of spermatozoa for fertilization. See also egg membrane.

Subjects: Medicine and Health — Biological Sciences.

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