Baer, Carl Ernst von, the greatest of modern embryologists, was born in 1792 in Esthonia, and was educated at Dorpat and Wurzburg. He was fifteen years professor in the university of Konigsberg, and then for nearly thirty in that of St. Petersburg, retiring in 1864. He died in 1876. In 1827 Baer discovered the mammalian ovum; and in his great work on the development of animals, of which the first part appeared in 1829 and the second in 1838, he showed the developmental basis of Cuvier's division of animals into Radiata, Articulata, Mollusca, and Vertebrata; traced in detail the development of the chicken in the egg; and laid down the law, now known by his name, that a developing embryo resembles in succession those of successively higher types. This is now known as the parallelism of ontogeny and phylogeny. Baer recognised that this law of specialisation was of general application throughout Nature.