Xenopus embryos are opaque, precluding direct observation of their interiors. However, a simulated view of the interior can be achieved using fixed embryos imnaged using confocal microscopy. The movie below, a morph created from single images of fixed Xenopus embryos by Mike Danilchik (Oregon Health and Sciences Univ.), provides an overview of the embryo's interior during gastrulation in Xenopus. This sequence shows nicely how the blastocoel is displaced and ultimately completely obliterated as the involuting involvution of mesoderm occurs. at the same time, a new cavity, the archetneron, become visible.