gastrulation

1. (embryology, biology) The stage of embryo development at which a gastrula is formed from the blastula by the inward migration of cells.Examples: "The study of comparative embryology, nevertheless, would lead us to expect to find this germ layer arising by a process of gastrulation."; "1929, Proceedings of the South Dakota Academy of Sciences, Volumes 13-19, South Dakota Academy of Science, page 52, In the instances described by various observers and in the quadruple one described herein, these gastrulations no doubt began at different times, since the embryos are of different sizes."; "2020, Konner M. Winkley, et al., 8: Tunicate Gastrulation, Lilianna Solnica-Krezel (editor), Gastrulation, Elsevier (Academic Press), page 227, Pharmacological inhibition of RhoA at later steps of gastrulation causes the apical constrictions to relax, indicating a persistent requirement for this pathway."