blastopore A mouth-like opening of the archenteron on the surface of an embryo in the gastrula stage. In many animals the blastopore becomes the anus, although in some it closes up at the end of gastrulation and may appear again at or near the same site. The blastopore is formed by an inward movement of the endoderm and mesoderm cells of the archenteron during gastrulation. Sometimes this movement is incomplete, so that an open pore does not develop; this explains the primitive streak of a bird or mammal embryo during gastrulation. In that case it is referred to as a ‘virtual’ blastopore. See also DEUTEROSTOMY PROTOSTOMY.

blastopore See archenteron.