Development Lab. Biology 113. Yolk Distribution. Isolecithal Telolecithal. Holoblastic versus Meroblastic cleavage. Holoblastic cleavage , the complete division of the egg occurs in species whose eggs have little or moderate amounts of yolk, such as sea urchins and frogs
Gastrula in which the surface pushes into the interior at a point called the blastopore to form a tube that will become the digestive system.
In a gastrula the cells on the outside are ectoderm, those lining the inner tube are endoderm, and cells that migrate and multiply between these layers will become the mesoderm.