noun
- one of the three primary embryonic cell layers.
noun
n.
- Any of the three primary cellular layers, the ectoderm, endoderm, or mesoderm, into which most animal embryos differentiate and from which the organs and tissues of the body develop.
- Any of three cellular layers, the ectoderm, endoderm, or mesoderm, into which most animal embryos differentiate in the gastrula stage and from which the organs and tissues of the body develop through further differentiation.