<embryology> A layer of cells produced during the process of gastrulation during the early development of the animal embryo, which is distinct from other such layers of cells, as an early step of cell differentiation. The three types of germ layers are the endoderm, ectoderm, and mesoderm.

Diploblastic organisms (e.g. Coelenterates) have two layers, ectoderm and endoderm, triploblastic organisms (all higher animal groups) have mesoderm between these two layers.

Germ layers become distinguishable during late blastula/early gastrula stages of embryogenesis and each gives rise to a characteristic set of tissues, the ectoderm to external epithelia and to the nervous system for example: although some tissues contain elements derived from two layers.

This entry appears with permission from the Dictionary of Cell and Molecular Biology

(11 Mar 2008)

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