gastrulationEmbryol.|gæstruːˈleɪʃən| [f. gastrula + -ation.] The formation of a gastrula. 1879tr.Haeckel's Evol. Man I. viii. 199 The formation of the Gastrula, or gastrulation.1887A. C. Haddon Introd. Embryology ii. (heading), Segmentation and gastrulation.