gastrulation

An early phase of embryonic development characterize by the development of three cell layers the provide the foundation for the development of the ectoderm (the outer layer from which Epidermis, hair, nails, brain, spinal cord, and peripheral nerves develops), mesoderm (the middle layer form which the muscles, bones, connective tissues, the heart, blood vessels, and the kidneys develop). and endoderm (the inner layer from which the linings of the digestive and respiratory tracts, as well as associated organs like the liver and pancreas develop).