Baer, Karl Ernst von, 1792–1876, Estonian biologist. He was a professor at Würzburg and Königsberg and from 1834 at St. Petersburg. Considered a founder of modern embryology, he discovered the notochord as well as the mammalian ovum. In his History of the Development of Animals (2 vol., 1828–37) he presented the theory of embryonic germ layers (the development of body tissues and organs from definite layers of cells formed in the early embryonic stages) and showed that the development of the embryo in different animals is similar in its early stages. He made these ideas a basis for a general evolutionary theory.
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