Lexic.us

Definition of Germ layer

1. Noun. (embryology) any of the 3 layers of cells differentiated in embryos following gastrulation.

Definition of Germ layer

1. Noun. (context: embryology) A collection of cells assembled during embryogenesis that eventually develop into all tissues and organs via organogenesis in animals. ¹

¹ Source: wiktionary.com

Medical Definition of Germ layer

1. 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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Literary usage of Germ layer

Below you will find example usage of this term as found in modern and/or classical literature:

1. Text-book of the embryology of man and mammals by Oscar Hertwig, Edward Laurens Mark (1905)
"THE outer germ-layer has for a long time also borne the name dermo-sensory layer. ... In this region the cells of the outer germ-layer grow out into long ..."

2. A Manual of Histology by Salomon Stricker (1872)
"The germ-membrane, according to him, consists of a layer of granules, constituting the foundation from which later the under germ- layer will be formed. ..."

3. Clinical Rheumatology: A Problem-oriented Approach to Diagnosis and Management by Roland W. Moskowitz (1921)
"The red dots mark the limit of the mesoderm: ak, outer germ layer (blue); mw, medullary ridges or folds; ff, neural tube; am, amniotic fold; t'o/, hof, so/, ..."

4. The evolution of man: a popular exposition of the principal points of human by Ernst Heinrich Philipp August Haeckel (1897)
"The important process of fission in the middle germ-layer which occasions ... At first the extent of this middle germ-layer is co-extensive with that of the ..."

5. Text-book of the Embryology of Invertebrates by Eugen Korschelt, Karl Heider, Edward Laurens Mark, William McMichael Woodworth, Matilda Bernard, Martin Fountain Woodward (1899)
"Cleavage and Formation of the Germ-layer. The cleavage of the egg in Scorpions is discoidal. At the pole of the egg, which is directed from the follicle ..."

6. The Unity of the Organism; Or, The Organismal Conception of Life by William Emerson Ritter (1919)
"7 * The Exact Mode of Involvement of the Germ-plasm Theory in the Germ-Layer Theory We return now to the immediate point, namely that of the way the ..."

7. The Unity of the Organism; Or, The Organismal Conception of Life by William Emerson Ritter (1919)
"7 * The Exact Mode of Involvement of the Germ-plasm Theory in the Germ-Layer Theory We return now to the immediate point, namely that of the way the ..."

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