The three primary germinal cell layers formed during gastrulation that line the central cavity of the gastrula, and which are partially determined in their developmental potential. Ectoderm, the outermost layer, gives rise to the nervous system and outer integument. Mesoderm, the middle layer, produces muscles, connective tissues, and the urogenital system. Entoderm, the innermost layer, differentiates into the alimentary tract and other internal organs (e.g., the liver).
See Adrenal medulla, Blastopore, Ectoderm, Entoderm (or endoderm), Gastrula, Gastrulation, Mesenchyme, Mesoderm. Oogenia, Organogenesis