met·a·neph·ros 
(mĕt′ə-nĕfrŏs′)
(mĕt′ə-nĕfrŏs′)n.
The third and final excretory organ that develops in a vertebrate embryo. In birds, reptiles, and mammals it replaces the mesonephros as the functional excretory organ and develops into the adult kidney.
[META- + Greek nephros, kidney.]
met′a·nephric (-rĭk) adj.