| The Columbia Encyclopedia, Sixth Edition. 2001-07. |
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| endoderm |
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( n´d dûrm´´) (KEY) , in biology, inner layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball. Cell movement results in an invagination of the bottom region, or vegetal hemisphere, of the embryo so that it resembles a double-walled cup. The inner layer of the cup is the endoderm; the outer layer is the ectoderm; a middle layer, the mesoderm, forms from a marginal zone. The endoderm is the germ layer from which are formed the digestive system, many glands, and part of the respiratory system. See embryo. |
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| | | The Columbia Encyclopedia, Sixth Edition. Copyright © 2007 Columbia University Press. |
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