gastrulating

/ˈɡæstrəˌleɪtɪŋ/
verb
  1. The process during embryonic development in which the blastula folds inward to form a gastrula, establishing the three germ layers.
    • When the embryo starts gastrulating, the future body plan begins to take shape.
    • Scientists observed the frog embryo gastrulating under the microscope.
    • The embryo is gastrulating as cells begin to migrate inward.