In the process of gastulation, the cells of the blastomere form a two-layered nerate and spherical structure. This is called gastrula dasha. The gastrula of hydra is called stereogastula because it is attached to the mother body. The outer layer of the gastrula is called ectoderm and the inner layer is called endoderm. Between the ectoderm and endoderm are jelly-like acellular mesoglia. The gastrular cavity is called the primitive cilenteron.