Gastrulation of frog larva or Xenopus

The cross-section of a frog embryo shows it at the blastula stage, characterized as a ball of cells with a fluid-filled cavity known as the blastocoel. The blastula has large yolk-filled cells at the vegetal pole and smaller cells at the animal pole, alongside the early establishment of the three germ layers: endoderm (yellow), mesoderm (red), and ectoderm (blue). During gastrulation, surface cells, referred to as bottle cells, move inward, leading to the formation of the dorsal lip and the internal movement of cells, creating the primitive gut or archenteron, surrounded by endodermal tissue. The cavity connects to the exterior through the blastopore, which later develops into the anus. As gastrulation progresses, the ectoderm envelops the embryo, while specific fates of the germ layers are defined: endoderm develops into the digestive and respiratory tracts, mesoderm contributes to the skeleton and circulatory systems, and ectoderm forms the skin, sense organs, and nervous system.