noun. double-walled stage of the embryo resulting from invagination of the blastula; the outer layer of cells is the ectoderm and the inner layer differentiates into the mesoderm and endoderm.
1. Noun, singular or mass These cells are called the gastrula, and over the course of the duck's incubation, they will develop to form the different parts of his body, like his lungs, muscles, nerves and skin.
