endoderm (ĕn´dədûrm´), 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.

endoderm (end-oh-derm) n. the inner of the three germ layers of the early embryo, which gives rise to the lining of most of the alimentary canal and its associated glands, the lining of the bronchi and alveoli of the lung, and most of the urinary tract.
—endodermal (en-doh-der-măl) adj.

endoderm (entoderm) The internal layer of cells of the gastrula, which will develop into the alimentary canal (gut) and digestive glands of the adult. See also germ layers.

endoderm In an embryo, the innermost layer of cells that gives rise to the lining of the archenteron (digestive cavity) and its associated glands. See also GASTRULATION.