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.

Where does the blastopore develop?

The blastopore is the first opening in the embryo – the point of invagination during gastrulation. The blastopore will eventually become either the mouth or the anus. One end of the gut-tube or the other. The space that forms during this time is the primitive gut, the archenteron.

What stage does the blastopore form?

Both the archenteron and blastopore are formed during the gastrulation stage of embryonic development. During gastrulation, the archenteron develops into the digestive tube (primitive gut), with blastopore becoming either anus or mouth depending on the organism.