ancestral vertebrate kidney, retained by larvae of hagfish and of some caecilians and occurring in the embryos of higher animals. Two tubes, the archinephric, or Wolffian (Wolffian duct), ducts, extend between the body cavity and the back and lead to the exterior. A series of tubules, one pair for each body segment, connects the body cavity with the Wolffian ducts. Each tubule is ciliated where it opens into the body cavity, and a knot of capillaries occurs at each of these openings, which are called nephrostomes.

The three types of adult-vertebrate kidneys develop from the embryonic archinephros: the pronephros from the anterior section, the mesonephros from the middle section, and the metanephros from the hind section.