Cuvier, however, as a strict matter-of-fact man, was incapable of appreciating the speculative conclusions which were drawn by his contemporaries Saint-Hilaire and Lamarck. On the contrary, he firmly stuck to the doctrine of the immutability of species; and, in order to account for the existence of animals whose kind exists no longer, he invented the famous doctrine of successive cataclysms.
Karl Ernst von Baer was born in 1792 in Esthonia, studied at Dorpat and then at Würzburg, where Döllinger introduced him to comparative anatomy. For a few years he was a Privat-docent at Berlin; then he went to Königsberg as Professor of Zoology and Embryology. In 1834 he became an Academician at St. Petersburg, where for many years he was occupied with the most varied studies, chiefly geographical and ethnological. The last years of his long, active life he spent in contemplative retire-
