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egg composed of shell and membranes that create a protected environment in which the embryo can develop out of the water
outermost membranous sac enclosing the embryo in higher vertebrates (reptiles, birds and mammals)
thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)
vascular fetal membrane that develops from the hindgut in embryonic higher vertebrates (reptiles, birds and mammals)
a fibrous scleroprotein that occurs in the outer layer of the skin and in horny tissues such as hair feathers nails and hooves
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