Exogastrulation

an experimentally induced disturbance of the process of gastrulation in animal embryos, effected, for example, by the removal of the egg membranes or a change in the pH of the medium. Exogastrulation consists in a change in the direction of morphogenetic movements of cells and cell layers of the embryo. In amphibians, for example, the material of the chordomesoderm and the endoderm, which normally goes inside the embryo, moves to the outside and has no contact with the exoderm over almost its entire surface. In the subsequent development of the exogastrulated embryo, the nervous tissue in the ectoderm does not become differentiated. An atypical epidermis is formed, while the material of the chordomesoderm and the entoderm undergoes differentiation.

Exogastrulation demonstrates the necessity of contact between the chordomesoderm and the ectoderm for induction of the rudiment of the nervous system. It also shows that various morpho genetic movements must be coordinated for the normal course of gastrulation.