A pit-like thing in the side of the embryo, through which cells fated to be endodermal, flow so that they leave the outer surface of the embryo and can create a new inner surface is called the blastopore.
It is a mouth-like opening of the archenteron on the surface of the embryo during the invagination of the archenteron.
In many animals, the Blastopore becomes the anus.
The Blastopore in embryology deals with the prenatal development stage of gametes through fertilization, embryo formation, and fetuses.