STRUCTURE AND GEOGRAPHICAL DISTRIBUTION. 55 



their families, and their genera, as far as they have repre- 

 sentatives elsewhere, bear everywhere the same identical 

 ordinal, family, or generic characters. The arctic foxes 

 have the same dental formula, the same toes and claws, in 

 fact, 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 and 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 then 1 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 structural 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 complication of the glands, 

 etc., etc. ; to peculiarities, indeed, which nobody but a 

 professional naturalist conversant with microscopic ana- 

 tomy would ever believe could present such precise and 

 permanent characters. So complete, indeed, is this iden- 

 tity, that, were any of these beings submitted to the 

 investigation of a skilful 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 family, but even its genus, could be iden- 

 tified as precisely as if it were perfectly well preserved in 

 all its parts. Were the genera, which have a wide range 

 upon the earth and in the ocean, few, this might be con- 

 sidered as an extraordinary case ; but there is no class of 

 animals and plants which does not contain many genera, 

 more or less cosmopolitan in their geographical distribution. 



