SKETCH 



HISTORY OF THE MAMMALIA. 



Order— RODENTIA. 



The difficulty of instituting a natural arrangement (that 

 is, an arrangement exhibiting the multiform links and 

 affinities of different groups) is confessedly great ; but 

 peculiarly so as it respects the component parts of the 

 present order. In itself, indeed, this order is definite, 

 and based upon characters which form a clear line of 

 separation between it and every other; but when we 

 come to investigate the species it embraces, we soon 

 feel ourselves perplexed among a multitude of forms, 

 and begin to hesitate at every step. Hence it is that no 

 two naturalists have arranged the Rodentia in the same 

 manner ; nay, Cuvier himself, in the last edition of his 

 ' Regne Animal,' set aside the principles by which in 

 his eai'lier edition he was guided, and followed out other 

 views. 



Among those naturalists who have lately devoted their 

 attention to the Rodentia, Mr. Waterhouse takes a fore- 

 most place ; and his arrangement, founded on the truest 

 philosophical principles, is a decided step in the advance- 

 ment of this department of Zoology. It would be out 

 of place, in a work like the present, to follow this natu- 

 ralist through his train of researches, but we may give 

 an outline of their results. Mr. Waterhouse considers 



VOL. IV. B 



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