During the intrauterine life, three separate excretory systems arise successively.
The pronephros is nonfunctional and undergoes complete regression soon after its formation.
The mesonephros serves as a temporary excretory organ. The body of the mesonephros undergoes degenerative changes, but caudal parts of the mesonephric tubules and mesonephric duct persist in the male.
The third and definitive structure is the metanephros.
