Note:  Do not rely on this information. It is very old.

Gastrola

Gastrola, the name of the stage in development which is passed through by all Metazoa or multicellular animals. It consists of a simple spherical or egg-shaped sac, composed of a double layer of cells with an opening (the blastopore) at one end. In one group of animals (the Gastreadse) the adult condition is not more advanced than this. [See Blastosphere for the general sketch of the The most important characters only are mentioned. early development.]