The yolk sac, which appears early in development, is ultimately connected to the developing gut tube. In early development, cells in the posterior wall of the yolk sac form the first fetal blood cells and blood vessels (angiogenic cell clusters). In addition cells from the epiblast migrate into the wall of the yolk sac and later migrate into the body of the embryo to form primordial germ cells that seed the developing gonads. The connection between the gut and yolk stalk may persist after birth as a Meckel's diverticulum.

Stacks Image 17