in·vag·i·na·tion /-ˌvæʤəˈneʃən/
  凹入; 內陷; 反折; 折入; 套?
  in·vag·i·na·tion /-ˌvæʤəˈneʃən/ 名詞
  In·vag·i·na·tion n.
  1. Biol. The condition of an invaginated organ or part.
  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.
  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.
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  invagination
       n 1: the condition of being folded inward or sheathed [syn: introversion]
       2: the folding in of an outer layer so as to form a pocket in
          the surface; "the invagination of the blastula" [syn: introversion,
           intussusception, infolding]