Answer :
The onset of gastrulation is signaled by the formation of the primordial streak, a groove in the caudal end of the epiblast layer.
What happens during the first opening of gastrulation?
In the blastopore The embryo's first opening, or blastopore, is where invagination occurs during gastrulation. Eventually, the mouth or the anus will develop from the blastopore. Either one or the other end of the gut-tube. The archenteron, a rudimentary gut, develops at this period.
In what part of the blastula does gastrulation begin?
The embryo's posterior side is where the extraembryonic tissue and epiblast converge, and this is where the primitive streak develops at the start of gastrulation. This is also where ingression occurs.
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