【医】 外包内陷

Invagination \In*vag`i*na"tion\, n. [L. pref. in- + vagina
sheath.]
1. (Biol.) 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.
[PJC]

3. Specifically: (Biol., 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.
[1913 Webster +PJC]

Note: 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.