Q. What is gastrulation? How during gastrulation are the first two germ layers formed? What are these germ layers?
Gastrulation is the process through which a portion of the blastula wall undergoes invagination inside the blastocele, forming a tube known archenteron (primitive intestine). The cells of the inner side of the tube form the cells of the outer side and the endoderm (germ layer) form the ectoderm (another germ layer). It is the start of the tissue differentiation in embryonic development.