What is gastrula?

Gastrula is embryo at the stage following the blastula, when it is a hollow cup-shaped structure having three layers of cells.It results by the process of gastrulation.which is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layered") structure known as the gastrula. These three germ layers are the ectoderm, mesoderm, and endoderm repectively.

Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layered") structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.
Gastrulation takes place after cleavage and the formation of the blastula and primitive streak. Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers.[3] Each layer gives rise to specific tissues and organs in the developing embryo. The ectoderm gives rise to epidermis, and to the neural crest and other tissues that will later form the nervous system. The mesoderm is found between the ectoderm and the endoderm and gives rise to somites, which form muscle; the cartilage of the ribs and vertebrae; the dermis, the notochord, blood and blood vessels, bone, and connective tissue. The endoderm gives rise to the epithelium of the digestive system and respiratory system, and organs associated with the digestive system, such as the liver and pancreas.