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That part of an embryo which represents the young stem; the caulicle or radicle.

alters its general character and mode of life, as in the development of the germ into the embryo, the egg into the animal, the larva into the insect (metamorphosis), etc.; also, the change which the histological units of a tissue are prone to undergo. See Metamorphosis.

An embryonic insect which has twice cast its skin previous to hatching from the egg.

rentiated; specifically (Biol.), homogenous, or nearly so; -- said especially of young or embryonic tissues which have not yet undergone differentiation (see Differentiation, 3), that is, which show no visible separation into their different structural parts.

iducts of many invertebrates in which the eggs are retained until they hatch or until the embryos develop more or less. See Illust. of Hermaphrodite in Append.

l clefts (Anat.), transverse clefts on the sides just back of the mouth in the vertebrate embryo, which open into the pharyngeal portion of the alimentary canal, and correspond to the branchial clefts in adult fishes.

covered, or first described, by Caspar Friedrich Wolff (1733-1794), the founder of modern embryology. Wolffian body, the mesonephros. -- Wolffian duct, the duct from the Wolffian body.

That part of biology which relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct.