42 ESSAY ON CLASSIFICATION 



where else representatives of different types living together. The 

 arctic Mammalia belonging chiefly to the families of Whales, Seals, 

 Bears, Weasels, Foxes, Ruminants and Rodents, have, as Mammalia, 

 the same general structure as the Mammalia of any other part of the 

 globe, and so have the arctic Birds, the arctic Fishes, the arctic Ar- 

 ticulata, the arctic Mollusks, the arctic Radiata when compared to 

 the representatives of the same types all over our globe. This identity 

 extends to every degree of affinity among these animals and the plants 

 which accompany them; their orders, their families, and their 

 genera, as far as they have representatives elsewhere, bear every- 

 where 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 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 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 peculi- 

 arities, indeed, which nobody but a professional naturalist, con- 

 versant 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 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 identi- 

 fied 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 which have a wide distribution is even so 

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



