LOUIS AGASSIZ. 



251 



and rises at last above the water. The winds then bring to it seeds, 

 and plants are developed. Thus appears an island separated by a small 

 lagoon from the mainland, to which it will soon be united. Florida has 

 been entirely formed in this way by successive creations. The time 

 required to produce this peninsula, according to Agassiz, must have 

 been more than two hundred thousand years. 



At the same time that Agassiz undertook to du-ect these expeditions 

 he desired to make known the results of his researches and the labors 

 undertaken in his laboratories. The great collections he amassed at- 

 tracted his attention to all branches of the animal kingdom. The Ver- 

 tebrates, the MoUusks, the Ai-ticulates, the Eadiates, the relations of 

 these branches to each other, their mode of appearance and develop- 

 ment, were for him an incessant source of new observations, published 

 in numerous articles and memoirs. 



In 1857, he gave to the public the plan of a work to be called Con- 

 tributions to the Natural History of tJie United States. The popularity of 

 the professor was at that time so great that he immediately obtained 

 more than 2,500 subscribers. Four volumes of this work appeared in 

 succession.* 



The first monograph comprehended a comx)lete study of the Chelo- 

 nians, their anatomy, their distribution in the actual world and in geo- 

 logical history, the description of American genera and species, and the 

 embryology of the turtle. The second, in the preparation of which Mr. 

 Clark rendered active assistance, is upon the Acalephs, which form with 

 the Polyps and the Echinoderms the class Eadiata; they are divided 

 into Ctenophores, Discophores, and Siphonophores. Mr. Sonrel was the 

 artist of the magnificent plates which accompanied these two volumes. 

 A complete resume of the ideas and the principles of Agassiz relative to 

 the classification of the animal kingdom, serves as an introduction to 

 these monographs. 



"In the beginning of this chapter," he writes, "I have ah-eady stated 

 that classification ^eems to me to rest ux)on too narrow a foundation 

 when it is chiefly based upon structure. Animals are linked together 

 as closely by their mode of development, by their relative standing in 

 their respective classes, by the order in which they have made their 

 appearance upon earth, by their geographical distribution, and gener- 

 ally by their connection with the world in which they live, as by their 

 anatomy. All these relations should, therefore, be fully expressed in a 

 natural classification ; and though structure furnishes the most direct 

 indication of some of these relations, always appreciable under every 



* Contributious to the Natural History of tlie United States ; in quarto volumes, 

 with numerous plates. Volume I, Essay on Classification ; North American Testudi- 

 nata. 1857. Volume II, Embryology of the Turtle. 1857. Volumes III and lY, 

 Acalephs in general, CtenophorsB, Discophorte, Hydroidaj, Homologies of the Radiata. 

 1860-1832. The introduction to the first volume, "An Essay on Classification," was 

 republished under the author's direction, at London, in 185U, in 1 vol. 8vo., pp. 361. 



