 The functional embryonic kidney in anamniotes is the pronephros.Kerr coined the term ‘"opisthonephros"’ in 1919.In 1949, Hyman wrote the opisthonephros “has used up the mesomere tissue from which in amniotes both mesonephros and metanephros come.” Some accounts call opisthonephros the ‘mesonephros’, but the opisthonephros in anamniotes (lampreys, fish, and amphibians) differ considerably than the mesonephros in amniotes (reptiles, birds, and mammals).