The correct option is
D Gastrulation
Gastrulation is a process that places place after cleavage.(Cleavage is the series of synchronized mitotic cell divisions of the fertilized egg that results in the formation of the blastomeres and changes the single-celled zygote into a multicellular embryo). Gastrulation is a phase in embryonic development during which the single-layered blastula develops into a three-layered gastrula.
During gastrulation three germ layers are formed from the blastula, namely, ectoderm, mesoderm andendoderm. The formation of gastrula is due to the migration and specific rearrangement of the cells of blastula.
Epiboly: The epibolic morphogenetic movements occur only in the prospective ectodermal blastomeres, which have a inherent property of flattening and forming a cohering epithelial layer. Thus, epiboly may be referred to the motility displayed by amoebocytes.
Emboly: The embolic morphogenetic movements are concerned with inward migration of prospective chorda-mesodermal and endodermal blastomeres from the external surface of the blastula and their extension along antero-posterior axis of the developing embryo.
Involution: The formation of a gastrula by ingrowth of cells formed at the dorsal lip.