The video sequence below provides a computer simulation of the behavior of the deep cells of the dorsal involuting marginal zone (DIMZ) in relation to surrounding tissues during Xenopus gastrulation. First, note that the IMZ is a torus (doughnut) of tissue containing deep, non-epithelial cells and superficial epithelial cells. The deep cells of the DIMZ undergo massive convergence and extension to extend dramatically on the dorsal side, forming axial mesoderm, including notochord and somites. At the same time, the superficial cells of the DIMZ form the roof of the archenteron (shown here in green), and are therefore endoderm. The non-involuting marginal zone (NIMZ) remains on the exterior, and forms ectoderm.