Invagination /(?)/

In·vag·i·na·tion

Invagination

n.
  1. The condition of an invaginated organ or part. (Biol.)
  2. The inward movement of the wall of a tissue or cell, to form a cavity; also, the cavity thus formed.
  3. The inward movement of one part of the wall of a blastula, to form a gastrula; the process of gastrulation, in which layers of the ovum are differentiated. (Biol., Embryology)