Final answer:
Gastrulation is the process by which the cells of the epiblast migrate to form the three primary germ layers: the ectoderm, mesoderm, and endoderm, each giving rise to different cells and organs in the body.
Step-by-step explanation:
The process by which the cells of the epiblast migrate and form the three primary germ layers is called gastrulation. During the second week of embryonic development, after fertilization, the embryoblast differentiates into the epiblast and hypoblast, setting the stage for gastrulation. By the end of the second week, cells of the epiblast begin to migrate at the primitive streak, a process that leads to the formation of a three-layered (trilaminar) embryonic disc. These layers are known as the ectoderm, mesoderm, and endoderm. The ectoderm will become the skin and nervous system, the mesoderm will develop into the bones, muscles, and heart, and the endoderm will give rise to most internal glands and organs including the gastrointestinal tract, liver, pancreas, and lungs.