This mass of mesoblastic cells may be called the metanephric blastema.
metanephros met·a·neph·ros (mět'ə-něf'rəs, -rŏs')
n. pl. met·a·neph·roi (-roi')
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.