Agassiz, Jean Louis Rodolphe, the greatest ichthyologist of this century, was born at Motier, on the Lake of Morat, in Switzerland, May 28th, 1807, where his father was pastor, his mother being the daughter of a physician. As a boy he kept pets of all kinds, including fish. He was educated at the gymnasium at Bienne, the academy at Lausanne, the medical school at Zurich, and at the universities of Heidelberg and Munich. At Heidelberg he had Tiedemann, the anatomist, Leuckart, the zoologist, and Bronn, the paleontologist, as his teachers, and Schimper and Braun, whose sister, Cecile, afterwards became his first wife, as fellow-students; and at Munich he lodged with Dollinger, the embryologist, and attended lectures by Martius, Schelling, and Oken. In 1829 Agassiz took his degree as Doctor of Philosophy at Erlangen, and in 1830 that of Doctor of Medicine at Munich, though not wishing to practise. He was entrusted by Martius with the description of the fishes collected during the Brazilian voyage, the publication of which served as an introduction to Cuvier and Humboldt on his visiting Paris in 1831. Here he attended Cuvier's last lectures, and imbibed his teleological and anti-evolutionary opinions, receiving also from him all his notes and drawings relating to fossil fish. In 1832 he became Professor of Natural History at the newly organised Lyceum at Neuchatel, a chair which he retained until 1840. During this period he produced his chief work, the Recherches sur les Poissons Fossiles, in five volumes, with 311 plates, describing 20,000 specimens, belonging to 1,700 species, contained in eighty of the chief museums of Europe. In this work he uses the scales as a basis of classification, establishing the order of "Ganoids," and points out the correspondence between the development of an individual fish and the succession of types of fish-structure in geclogical time. During the progress of this work he became a member of the French Academy of Sciences and of the Royal Society, visiting England in 1834, 1835, and 1840. In 1836 he adopted Charpentier's views as to the former greater extension of the glaciers of the Alps, and subsequently propounded the theory of a Glacial Period (q.v.), converting Buckland and Lyell to his views, as published in his Etudes sur les Glaciers (1840) and Systeme Glaciaire (1846), and showing glacial action to have occurred in Scotland, Wales, and the Lake District. With the help of Desor he completed, in 1842, his Monographic d'Echinodermes Vivans ct Fossiles, and in 1845, with that of Karl Vogt, his Freshwater Fishes of Central Europe. In 1846, with the assistance of many other naturalists, he issued his Nomenclator Zoologicus, which was supplemented in 1848 by the Bibliographia Zoologia and Gcologia. In 1846 Agassiz went to America, originally on a temporary lecturing tour, but, as it proved, for the remainder of his life. He aroused a remarkable enthusiasm for scientific research; a chair was endowed for him at Harvard; and government steamers were placed at his disposal for coast dredging. In 1857 he issued the first volume of his Contributions to the Natural History of the United States, containing the celebrated Essay on Classification, his last great work. The Museum of Comparative Anatomy at Harvard, established in 1859, now became the chief object of his life. In 1865 he made a journey in search of health and specimens to Brazil, accompanied by his second wife (nee Gary), and in 1871 he made a cruise right round South America, in the Hassler. On his return, Mr. John Anderson presented him with Penikese lsland, for a school of marine zoology, and he had just successfully launched this, his final idea, when his life of unremitting scientific toil ended peacefully at Cambridge, Mass., 14th December, 1873.