gastrulation

n. stage in the development of a fetus (Biology)

Gastrulation is a phase early in the development of animal embryos, during which the morphology of the embryo is dramatically restructured by cell migration. Gastrulation varies in different phyla. Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers.
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Gastrulation /gas·tru·la·tion/ the process by which a blastula becomes a gastrula or, in forms without a true blastula, the process by which three [more]Gastrulation - Community and Resources

Noun
1. the process in which a gastrula develops from a blastula by the inward migration of cells
(hypernym) organic process, biological process
(part-holonym) growth, growing, maturation, development, ontogeny, ontogenesis

n. gastrulation, stage in the development of a fetus (Biology)