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ON THE ARRANGEMENT OF THE MAMMALIA. 



SOME explanation of the plan adopted in the arrangement of the 

 Mammalia is here obviously necessary ; and this without entering into 

 abstruse disquisitions, or perplexing details : the results, therefore, of an 

 investigation of the subject, rather than the steps by which such results 

 are attained, will alone be presented. It would, however, be unpardon- 

 able to omit, altogether, reference to the views of other naturalists ; 

 hence, a brief outline of the systems of Ray, Linnaeus, Illiger, Cuvier, and 

 others, will be adduced. It must, then, be premised, that every animal 

 has its own characters, by which it is distinguished, and which constitute 

 it a species. Each species consists of individuals. Individuality is the 

 ultimate division ; and when we designate a species, we include, in that 

 title, every similar individual. Thus, when we call the Tiger a species, 

 we include, in that word, every Tiger, one being the representative, or 

 prototype, of all. In the next place it may be stated, that, by a sponta- 

 neous act of synthesis, the mind cannot but associate, in idea, such species 

 as appear most nearly to resemble each other. We associate, for example, 

 the Tiger and the Leopard, because we perceive, at once, their mutual 

 affinity ; and animals, thus collocated, are regarded as forming a group, 

 more or less natural, according to the value of the affinities by which 

 it is bonded together. If truly natural, it will consist of species, agreeing 

 in every character, except such as merely serve to draw a line of specific 

 distinction between them, and which are, consequently, of a trivial or 

 superficial nature (as size, colour, length of fur, or shape and number of 

 scales, or plates, length of snout, ears, tail, &c.) ; while a sameness of 

 general form, habits, and manners prevails. A group thus consisting of 

 closely allied animals is termed a genus. 



Again, there are genera which agree, in various structural characters, 

 with other genera ; and these are associated into what are termed families. 

 But families have, again, certain structural grounds of union with other 

 families, and these constitute orders. The assemblage of orders, all agree- 

 ing in essential modes of organization, constitutes a class. The chafacters 

 of the class Mammalia, the subject of the present work, have been already 

 detailed. 



Now, as is very evident, the ideas we form of an order must be more 

 comprehensive than those attaching to the subordinate sections, according 

 to their respective grades ; for the ratio of alliance, both as depending 

 upon external and internal structure, diminishes as we proceed from 

 genera upward. The progressive enlargement of groups, by the union of 

 genera, so as to form families, and of families so as to form orders, is 

 necessarily attended by a parallel diminution of the aggregate of characters 



