A-A”: Gastrulation by furrow formation employed by Drosophila, and Tribolium in the anterior segments. B-B”: Gastrulation mode found in the segments deriving from the growth zone of Tribolium. A multilayered mass of cells loses its epithelial character and is internalized by the migration of the lateral ectodermal cells. C-C”: Hymenopteran mode of gastrulation, where the mesoderm forms a stiff plate, the ectoderm breaks contact with mesoderm and migrates ventrally until the free edges meet and fuse at the ventral midline. Blue= lateral ectoderm, Green=mesectoderm, Red= mesoderm precursors expressing twist, Pink= mesoderm precursors not expressing twist. Other cell fates have been omitted for clarity.