According to every textbook of embryology, an early mouse embryo is composed of two cell layers: the epiblast (ectoderm) and the visceral endoderm, which covers the epiblast. During gastrulation ...

After a sperm fertilizes an egg, the totipotent cell divides into a zygote. As division continues, some cells divide into the growing mass, distinguishing cells that form the embryo (epiblast) from ...