Embryonic development involves cell division, differentiation, and morphogenesis. Cell division results in an increase in the number of cells. All the cells result from mitotic divisions beginning with the zygote. Differentiation is the development of specialized cells that are organized into tissues and organs. Morphogenesis includes the physical processes that give shape to the animal's body and organs.
Fertilization forms the diploid zygote and triggers the onset of embryonic development.
When the head of the sperm contacts the egg the enzymes are released from a vesicle via exocytosis. This allows the arcosomal process to elongate and penetrate the the jell coat of the egg. The protein coating the tip will attach to the exact receptors on the egg's vitelline layer to ensure it is the correct species of sperm. The enzymes continue to digest the membrane allowing ti tip to reach the plasma membrane of the egg. The two membranes fuse, allowing the sperm's nucleus to enter the egg.