Cleavage stages of embryogenesis are typically very similar across animals. During cleavage, a single cell embryo rapidly divides to form a ball of cells, called a blastula. This ball may be hollow in...Cleavage stages of embryogenesis are typically very similar across animals. During cleavage, a single cell embryo rapidly divides to form a ball of cells, called a blastula. This ball may be hollow inside, have a hollow region, or be fairly solid. Gastrulation refers to a time of great flux in animal embryos. During gastrulation the cells produced during cleavage begin to move relative to each other. As they move, they change their local environment and come into contact with new cells.
