38 ESSAY ON CLASSIFICATION. Part I. 



dental formula, the same toes and claws, in flict, every generic peculiarity which 

 characterizes foxes, whether they live in the Arctics, or in the temperate or tropical 

 zone, in America, in Europe, in Africa, or in Asia. This is equally true of the seals 

 or the whales; the same details of structure which characterize their genera in the 

 Arctics reappear in the Antarctics, and the intervening space, as far as their natural 

 distribution goes. This is equally true of the birds, the fishes, etc., etc. And let it 

 not be supposed that it is only a general resemblance. By no means. The struc- 

 tural identity extends to the most minute details in the most intimate structure of 

 the teeth, of the hair, of the scales, in the furrows of the brain, in the ramification 

 of the vessels, in the folds of the internal surface of the intestine, in the complica- 

 tion of the glands, etc., etc., to peculiarities, indeed, which nobody but a professional 

 naturalist, conversant with microscopic anatomy, would ever believe could present 

 such precise and permanent characters. So complete, indeed, is this identity, that 

 were any of these beings submitted to the investigation of a sldlful anatomist, after 

 having been mutilated to such an extent that none of its specific characters could 

 be recognized, yet not only its class, or its order, or its famUy, but even its genus, 

 could be identified as precisely as if it were perfectly well preserved in all its parts. 

 Were the genera few which have a wide range upon the earth and in the ocean, 

 this might be considered as an extraordinary case ; but there is no class of animals 

 and plants which does not contain many genera, more or less cosmopolite in their 

 geographical distribution. The number of animals Avhich have a wide distribution is 

 even so great that, as far at least as genera are concerned, it may fairly be said, 

 that the majority of them have an extensive geographical range. This amounts to 

 the most complete evidence that, as far as any of these genera extends in its geo- 

 graphical distribution, annuals the structure of which is identical within this range of 

 distribution, are entirely beyond the influence of physical agents, unless these agents 

 have the power, notwithstanding their extreme diversity, within these very same 

 geographical limits, to produce absolutely identical structures of the most diversified 

 types. 



It must be remembered here, that there are genera of Vertebrata, of Articulata, 

 of Mollusks, and of Radiata, which occupy the same identical and wide geographical 

 distribution, and that while the structure of their respective representatives is identi- 

 cal over the whole area, as Vertebrata, as Articulata, as MoUusks, as Radiata, they 

 are at the same time built upon the most different plans. I hold this fact to be in 

 itself a complete demonstration of the entire independence of physical agents of the 

 structure of animals, and I may add that the vegetable kingdom presents a series of 

 tacts identical with these. This proves that all the higher relations among animals 

 and plants are determined by other causes than mere physical influences. 



