Germ Layers

Germ Layers

This image is based on article Germ Layer by MacCord, Kate

A germ layer is a group of cells in an embryo. Those layers interact with each other as the embryo develops and will eventually give rise to all of the organism’s organs and tissues. Almost all animals initially form two or three germ layers. The germ layers develop early in embryonic life, through the process of gastrulation. During gastrulation, a hollow cluster of cells called a blastula reorganizes into two primary germ layers: an inner layer, called endoderm, and an outer layer, called ectoderm. In all animals, except for organisms of the phylum Cnidaria, the endoderm and ectoderm interact to produce a third germ layer, called mesoderm.


  1. Gilbert, Scott. Developmental Biology. Massachusetts: Sinauer, 2006.
  2. Hall, Brian Keith. "Germ Layers and the Germ Layer Theory Revisited." Evolutionary Biology30 (1997): 121–86.
  3. Kenyon College Biology Department. “Gastrulation.” Kenyon College. (Accessed August 2, 2019).

How to cite

MacCord, Kate, "Germ Layers". Embryo Project Encyclopedia (2013-09-17). ISSN: 1940-5030

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Arizona State University. School of Life Sciences. Center for Biology and Society. Embryo Project Encyclopedia.


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Thursday, January 20, 2022 - 20:51


Theories, Processes


Germ Layers; Gastrulation; Embryology; Cell differentiation; Embryos; Cells; Tissues; Anatomy; Vertebrates; invertebrates; Embryological development; Organs; Organs (Anatomy); Blastula; Central nervous system; Pander, Christian Heinrich, 1794-1865; Rathke, Heinrich, 1793-1860; Baer, Karl Ernst von, 1792-1876; Huxley, Thomas Henry, 1825-1895; Lankester, E. Ray (Edwin Ray), Sir, 1847-1929; Haeckel, Ernst, 1834-1919; His, Wilhelm, 1831-1904; Spemann, Hans, 1869-1941; Nieuwkoop, Pieter D. (Pieter Dirk); Concept