Gastrulation

from WordNet (r) 3.0 (2006)

gastrulation
    n 1: the process in which a gastrula develops from a blastula by
         the inward migration of cells

from The Collaborative International Dictionary of English v.0.48

Gastrulation \Gas`tru*la"tion\ (g[a^]s`tr[.u]*l[=a]"sh[u^]n), n.
   (Biol.)
   The process of invagination, in embryonic development, by
   which a gastrula is formed.
   [1913 Webster]