what is invagination
Invagination is the infolding of one part within another part of a structure, a folding that creates a pocket.The term, originally used in embryology, has been adopted in other disciplines as well. Invagination is the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of cells, the blastula, into a multi-layered organism, with differentiated germ layers: endoderm, mesoderm, and ectoderm.