In zoology, an egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing embryo can survive on its own. The term “egg” is used differently outside the animal kingdom, for an egg cell. Reproductive structures similar to the egg in other kingdoms are termed...
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