Invagination
Invagination , noun
[Latin pref. in- + vagina sheath.]
1.
(Biology) The condition of an invaginated organ or part.
2.
The inward movement of the wall of a tissue or cell, to form a cavity; also, the cavity thus formed.
3.
(Biology, Embryology) 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.
In embolic invagination, one half of the blastosphere is pushed in towards the other half, producing an embryonic form known as a gastrula. -- In epibolic invagination, a phenomenon in the development of some invertebrate ova, the epiblast appears to grow over or around the hypoblast.