It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals.

[1] In humans, the mesonephros consists of units which are similar in structure and function to nephrons of the adult kidney.

Each of these consists of a glomerulus, a tuft of capillaries which arises from lateral branches of dorsal aorta and drains into the inferior cardinal vein; a Bowman's capsule, a funnel like structure which surrounds the glomerulus; and a mesonephric tubule, a tube which connects the Bowman's capsule to the mesonephric duct.

One end grows toward and finally opens into the mesonephric duct, the other dilates and is invaginated by a tuft of capillary bloodvessels to form a glomerulus.

In females, the mesonephros degenerates entirely, though vestigial structures such as Gartner's ducts, the epoophoron, and paroophoron are common.