Polarity in embryogenesis

In some cases, the animal pole is thought to differentiate into the later embryo itself, forming the three primary germ layers and participating in gastrulation.

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 amphibians, the development of the animal-vegetal axis occurs prior to fertilization.

[4] A pigment pattern provides the oocyte with features of a radially symmetrical body with a distinct polarity.

In fact, the axis polarity serves as one coordinate of geometrical system in which early embryogenesis is organized.