170 M. Agassiz on the Relations between Animals 



marine types among Turtles, which rank much higher than the 

 whole order of Batrachians, which are almost entirely fluviatile ; 

 and we find again marine and fluviatile types among Birds and 

 Mammalia, the highest of all Vertebrata. These facts show most 

 conclusively that an organization as high as that of the Vertebrata 

 — introducing a mode of existence so independent of the changes 

 of the seasons throughout the year, so durable as to last for num- 

 bers of years (whilst among Invertebrata, and especially among 

 Insects, but also among many other animals of lower type, there 

 exists the most intimate connection between their development 

 and the course of the seasons) ; we say these facts show, that with 

 such animals which are placed so far above the influence of phy- 

 sical conditions, their connection with the circumstances under 

 which they live is much weaker, so much so that internal struc- 

 ture overrules greatly the foundation of those connections which 

 are so intimate in lower animals, and reduces their limits to sub- 

 ordinate connections between members of the minor groups. 

 While in the class of Fishes — the lowest — the whole type is orga- 

 nized in such a manner as to make it uniformly dependent upon 

 one of the natural elements in which animals live, the three other 

 classes present most diversified combinations, there being marine, 

 fluviatile, and terrestrial or aerial types in these classes, under 

 the development of as many structural types, diff'ering almost in 

 the same degree when contrasted with each other, and so much, 

 that the aquatic Mammalia even in their marine types, or the 

 marine Turtles, difi'er as much from each other or from Birds as 

 they agree with their respective freshwater or terrestrial types. 

 These discrepancies between the great types may be owing to 

 other motives in the plan of creation than those to which they 

 are here ascribed. The apparent anomalies between some of the 

 articulated types may also be the results of combinations different 

 from those with which they are connected above. But whether 

 these views are correct or not, I have no doubt that the study of 

 the phsenomena which I am now contrasting, cannot fail to lead 

 finally to a more correct appreciation of the natural relations 

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

 than the vague views which have prevailed lately, from want of 

 investigation of the subject rather than from an especial view 

 taken of it. I am far from supposing that in every instance I 

 have hit at the outset the true view ; I shall be satisfied to have 

 called forth direct investigation upon this question, and led the 

 way in a field which promises such ample reward. 



Before entering into a special investigation of the natural rela- 

 tions of Vertebrata and the surrounding media, it may not be out 

 of place to call attention to some collateral facts which will appear 

 particularly prominent in the type of Vertebrata, but which have 



