pronephros

pronephros /pro·neph·ros/ (pro-nef´ros) pl. proneph´roi  

1. a vestigial excretory structure developing in the embryo before the mesonephros; its duct is later used by the mesonephros, which arises caudal to it.

2. the definitive excretory organ of primitive fishes.proneph´ric

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pro·neph·ros (pr-nfrs, -rs)

n. pl. pro·neph·roi (-roi) or pro·neph·ra (-r)

A kidneylike organ, being either part of the most anterior pair of three pairs of organs in a vertebrate embryo, usually disappearing early in embryonic development.

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pronephros

pl. pronephroi [Gr.] the primordial kidney; nonfunctional in mammals; functional only in amphioxuses and lampreys; an excretory structure or its rudiments developing in the embryo before the mesonephros; its duct is later used by the mesonephros, which arises caudal to it.