Epibolia

Epibolia

Epibolia is a process of embryonic development. It is one of the processes that leads to the formation of the gastrula during gastrulation. In epiboly, the micromeres, or small blastomeres, multiply rapidly and surround the macromeres, or large blastomeres, thus forming the ectoderm and endoderm.

Gastrulation by epiboly occurs normally when the egg has a moderate amount of yolk located at the vegetative pole, and cleavage produces large yolk macromeres. In this case, the blastocoel is more or less virtual (stereoblastula).