30 ESSAY ON CLASSIFICATION. Part I. 



every liojie to arrive at any satisfactory result upon this subject, did it not appear 

 now, that the inquiry must be circumscribed within different limits, to be conducted 

 upon its true ground. The results to which I have already arrived, since I have 

 perceived the mistake under which investigators have been laboring thus far, in 

 this respect, satisfy me that the point of view under which I have presented the 

 subject here is the true one, and that in the end, the characteristic gradation 

 exhibited by the orders of each class, will present the most striking correspondence 

 with the character of the succession of the same groups in past ages, and afFoi'd 

 another startling proof of the admirable order and gradation which have been estab- 

 lished from the very beginning, and maintained through all times in the degrees of 

 complication of the structure of animals. 



SECTION IX. 



RANGE OF GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 



The surface of the earth being partly formed by water and partly by land, and 

 the organization of all livino; being-s standino; in close relation to the one or the other 

 of these mediums, it is in the nature of things, that no single species, either of ani- 

 mals or plants, should be vmifonnly distributed over the whole globe. Yet there 

 ai'e some types of the animal, as well as of the vegetable kingdom, which are equably 

 distributed over the whole surface of the land, and others which are as widely scat- 

 tered in the sea, while others are limited to some continent or some ocean, to some 

 particular province, to some lake, nay, to some very limited spot of the earth's 

 surface.^ 



As far as the primary divisions of animals are concerned, and the nature of the 

 medium to which they are adapted does not interfere, representatives of the four 

 great branches of the animal kingdom are everywhere found together. Radiata, 

 Mollusks, Articulata, and Vertebrata occur together in every part of the ocean, in 

 the Arctics, as well as under the equator, and near the southern pole as far as man 

 has penetrated ; every bay, every inlet, every shoal is hamited by them. So univer- 



^ The human race aftbrds an example of the witle Ocean, how fishes may be circumscribed in the sea, 



distribution of a terrestrial type ; the Herring and and that of the Goniodonts of South America in 



the Mackerel fomilies have an equally wide distri- the fresh waters. The Chaca of Lake Baikal is 



bution in the sea. The JLammalia of New Hoi- found nowhere else ; this is equally true of the 



land show how some families may be limited to one Blindtish (Amblyopsis) of the Mammoth Cave, and 



continent ; the family of Labyrinthici of the Indian of the Proteus of the caverns of Carintliia. 



