anatomy. He next entered the University of Munich, where, in company with Martius, Oken, Döllinger, and Schelling, he devoted himself eagerly to the pursuit of natural history. At that time Martius was publishing his great work on the "Natural History of Brazil," arid, upon the death of Spix, who was editing the zoological portion, Martius intrusted to Agassiz the description of the fishes. In this work, which was admirably well done, Agassiz characterized nine genera, embracing forty-two species new to science.
For some time Agassiz had contemplated a monograph on the "Fresh-water Fishes of Central Europe," but pecuniary embarrassment rendered this impossible, till a bookseller by the name of Cotta, to whom Agassiz showed the material he had collected, furnished him the means necessary for its completion. Meanwhile he studied and obtained the degree of Doctor of Medicine at Munich, and of Doctor of Philosophy at Erlangen. After his examination, Agassiz went to Vienna, and applied himself closely to the study of actual and fossil ichthyology. From Vienna he went to Paris, where he made the acquaintance of Cuvier and Humboldt, both of whom warmly welcomed this expert young naturalist. Here he lived on the most intimate terms with Cuvier till the death of that naturalist, in 1832, when he returned to Switzerland and established himself at Neufchatel, where he was appointed Professor of Natural History, a position he held till his departure for America.
Through the influence of Humboldt, between whom and Agassiz there existed the warmest friendship, he was enabled to begin the publication of his "Poissons Fossiles," a work evincing such careful and profound research, and such a wonderful power of generalization, as to obtain for him a place among the very first naturalists of the day. This work, which appeared in parts, between the years 1833 and 1845, comprises five volumes, of about 1,700 quarto pages, with an atlas of 400 folio plates, and contains descriptions of nearly a thousand species of fossil fishes. Aside from the great number of species, genera, and families established, Agassiz adopted an entirely new system of classification. In the classification proposed by Cuvier, fishes were divided into two orders, according to the nature of the skeleton, viz., cartilaginous and osseous. Agassiz—looking upon the external covering of the animal as a reflex of the connection existing between the being and its surroundings, bearing the imprint of all the peculiarities of its existence, and consequently of its organization—deemed that the true principle of the classification of fishes was to be found in the scales. In view of this he proposed a division of the families of fishes into four orders, viz., Placoids, in which the scales are represented by plates of enamel, as in the sharks; Ganoids, in which the scales consist of angular bony plates covered with a thick layer of enamel, as in the gar-pikes; Ctenoids, or fishes with true scales, in which the posterior edges of the laminæ are toothed; and Cycloids, in which the scales are com-
