In some cases, the vegetal pole is thought to differentiate into the extraembryonic membranes that protect and nourish the developing embryo, such as the placenta in mammals and the chorion in birds.
In certain cases, the vegetal pole of an embryo is believed to develop into the extraembryonic membranes that provide protection and nourishment for the growing embryo, including the placenta in mammals and the chorioallantoic membrane in birds.