The embryonic stage of development in which the cells form a double-layered hollow sphere.
The second stage of the development of an embryo.
Early stage in embryo development occurring after the blastula stage; the gastrula is a hollow, cup-shaped structure consisting of an outer ectoderm layer and an inner layer that later differentiates into two layers (endoderm and mesoderm).
An early stage in the development of many animal embryos. It consists of a double-layered ball of cells formed by invagination and movement of cells in the preceding single-layered stage (blastula) in the process of gastrulation. It contains a central cavity, the archenteron, which opens through the blastopore to the outside. True gastrulation only occurs in the embryos of amphibians and certain fish, but a similar process occurs in the embryonic disk in other vertebrates, including man.
The stage in embryonic development following the blastula in which the embryo assumes a two-layered condition. The outer layer is the ectoderm or epiblast; the inner layer, the endoderm or hypoblast. The latter lines a cavity, the gastrocoele or archenteron, that opens to the outside through an opening, the blastopore.