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The excretory organ of the embryo, collective Wolffian tubules, which forms the urogenital fold from which the reproductive organs develop. The mesonephros is the permanent kidney in fish and amphibians, but atrophies in reptiles, birds, and mammals.

The intermediate part of the excretory organ in vertebrate embryos-it becomes the functional kidney in lower Craniata, it atrophies in the higher forms; the Wolffian body.

Syn.: corpus wolffianum. The wolffian body, or primordial kidney, the middle or largest division of the segmental apparatus of the embryo. In the female a portion of it persists as the epoophoron. See pronephros. [Gr.]