The process of pushing ventral surface of nematode embryo into the interior is known as

The process of pushing the ventral surface of nematode embryo into the interior is known as Epiboly.
Epiboly describes one of the five major types of cell movements that occur in the gastrulation stage of embryonic development of some organisms. It is the spreading and thinning of the ectoderm while the endoderm and mesoderm layers move to the inside of the embryo.