234 Agassiz on Zoological Classification. 



study of the relations of animals with the elements in which 

 they live, in ascertaining their natural relations among them- 

 selves ; but even in this respect we may derive valuable 

 hints from a careful study of the geographical distribution 

 of all animals ; and the mere nature of the elements in which 

 they live naturally. 



On reviewing lately the whole animal kingdom, with a 

 view to ascertain what is the value of the natural connection 

 between the animals and the media in which they live, with 

 reference to organic gradation, I have satisfied myself that 

 aquatic types are decidedly inferior to the terrestrial ; the 

 marine inferior to the lacustrine and fluviatile ones ; that 

 those which live upon the main-land and burrow under 

 ground are inferior to those which live above ground ; that 

 nocturnal are inferior to diurnal types ; and that, under 

 otherwise similar circumstances, representatives of one and 

 the same group which differ in these respects, have a higher 

 and lower rank, in accordance with their external circum- 

 stances ; so much so, that where we have no other guides, 

 an inference respecting their natural position may be fairly 

 derived from their conditions of life. 



It will thus be obvious, that as soon as we introduce simul- 

 taneously into our classification considerations derived from 

 all these difi^erent sources ; as soon as we allow the embry- 

 onic development, geological succession, geographical distri- 

 bution, and relation to the natural elements, to assist us in 

 our efforts to assign to all animals a natural position in one 

 great system, we shall be able to sketch a far more complete 

 picture of the great diversity which exists in nature, than if 

 we allow ourselves to be guided chiefly by anatomical data ; 

 and my object at present is mainly to urge the necessity of 

 studies in these different directions, with a view of improving 

 our classification, and to insist upon the necessity of keeping 

 in view, at the same time, all these facts, whenever we at- 

 tempt to form a correct idea of the manifested relations 

 which exist throughout the creation, as to all their different 

 types, from the earliest period of the existence of ani- 

 mals up to the present day. — Proceedings of the American 

 Association for the Advancement of Science, held at Charleston^ 

 South Carolina, March 1850. 



