The inner membrane surrounding the embryo in some arthropods and other organisms, lying beneath the outer protective membrane.
From endo- (within) + chorion (from Greek chorion, meaning 'membrane' or 'skin'). The chorion is an outermost membrane, and endo- specifies the inner layer when multiple membranes exist.
Embryonic membranes like the chorion were crucial to evolution—animals that developed these protective layers could reproduce away from water, fundamentally changing where life could exist on Earth.
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