A germ layer, occasionally referred to as a germinal epithelium, is a group of cells, formed during animal embryogenesis. Germ layers are particularly pronounced in the vertebrates; however, all animals more complex than sponges (eumetazoans and agnotozoans) produce two or three primary tissue layers (sometimes called primary germ layers). Animals with radial symmetry, like cnidarians, produce two germ layers (the ectoderm and endoderm) making them diploblastic. Animals with bilateral symmetry produce a third layer between these two layers (appropriately called the mesoderm) making them triploblastic. Germ layers eventually give rise to all of an animal’s tissues and organs through the process of organogenesis.
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Famous quotes containing the words germ and/or layer:
“I care not by what measure you end the war. If you allow one single germ, one single seed of slavery to remain in the soil of America, whatever may be your object, depend upon it, as true as effect follows cause, that germ will spring up, that noxious weed will thrive, and again stifle the growth, wither the leaves, blast the flowers, and poison the fair fruits of freedom. Slavery and freedom cannot exist together.”
—Ernestine L. Rose (1810–1892)
“This world is run by people who know how to do things. They know how things work. They are equipped. Up there, there’s a layer of people who run everything. But we—we’re just peasants. We don’t understand what’s going on, and we can’t do anything.”
—Doris Lessing (b. 1919)