GERM LAYER By N., Pam M.S. - May 11, 2013 One of three layers of cells in an animal embryo at the gastrula stage that organs and tissues develop. Outermost layer is the ectoderm, middle is mesoderm and is the endoderm. GERM LAYER: "A germ layer is seen in the embryo." Related Psychology Terms MESODERM EPIDERMIS NEURAL PLATE RETINA ECTODERM NEURAL NETWORKS GASTRULA CORTICAL LAYERS WEAR-AND-TEAR THEORY OF AGING CANCER Cite this page: N., Pam M.S., "GERM LAYER," in PsychologyDictionary.org, May 11, 2013, https://psychologydictionary.org/germ-layer/ (accessed July 12, 2020).