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Baer, Karl Ernst von

embryo skin mammalian develops

[bair] (1792–1876) Estonian embryologist: discoverer of the mammalian ovum.

Baer’s wealthy family was of German descent, so it was natural for him to study in Germany after graduating in medicine at Dorpat in Estonia. He taught at Königsberg in Germany from 1817–34, when he moved to St Petersburg. His best-known discoveries, however, were made in Königsberg. There, in 1826, he studied the small follicles discovered in the mammalian ovary by R de Graaf (1641–73) in 1673, and named after him; they had often been assumed to be mammalian eggs. Baer showed that the Graafian follicle of a friend’s bitch contained a microscopic yellow structure which was the egg (ovum). He identified structures within the embryo (the fertilized and developing egg), including the Page 23  notochord, a gelatinous cord which develops into the backbone and skull in vertebrates, and he found the neural folds (which later form the central nervous system). In 1817 C H Pander (1794–1865) had noted three layers of cells in the vertebrate embryo, which were to be named by in 1845 ectoderm (outer skin) mesoderm (middle skin) and endoderm (inner skin). These ‘germ layers’ each develop into specialized organs later (eg the mesoderm forms muscles and bones); Baer emphasized that the embryos of various species are at first very similar and may not be distinguishable and that, as it develops, the embryo of a higher animal passes through stages which resemble stages in the development of lower animals. This idea was later to be fruitful in embryology and in evolution theory.

Baer led expeditions to Arctic Russia to collect plant and animal specimens, studied fishes and collected human skulls (in 1859 he suggested that human skulls might have a common ancestral type, but he never supported ideas). His fame rests on his position as a founder of modern embryology.

Baeyer, Adolf von [next] [back] Badura-Skoda (real name, Badura)

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