

CHAPTEK XII. 



EODENTS. 



The rodents, psycliologically considered, are, of all orders 

 in the animal Idngdom, most remarkable for the differ- 

 ences presented by constituent species. For while the 

 group contains many animals, such as the guinea-pig, 

 whose instincts and intelligence cannot be said to rise 

 above the lowest level that obtains among mammalian 

 forms, it also contains other animals with instincts as 

 remarkable as those of the squirrel, intelligence as con- 

 siderable as that of the rat, and a psychological develop- 

 ment as unique as that of the beaver. In no other group 

 of animals do we meet with nearly so striking an exempli- 

 fication of the truth that zoological or structural affinity 

 is only related in a most loose and general way to psycho- 

 logical or mental similarity. Up to a certain point, 

 however, even here we meet with an exemplification of 

 what I may call a complementary truth, namely, that 

 similarity of organisation and environment is in a general 

 way related to similarity of instincts (though not neces- 

 sarily of intelligence). This is obviously the case with 

 the habit from which the order takes its name; for 

 whether the instinct of gnawing is here the cause or the 

 result of peculiar organisation, the instinct is unquestion- 

 ably correlated with the peculiarity. And similarly, though 

 less obviously, is this the case with the instinct of storing 

 food for winter consumption, which is more prevalent 

 among the rodents than in any other order of mammals — 

 rats, mice, squirrels, harvesters, beavers, &c., all mani- 

 festing it with remarkable vigour and persistency. Here 

 we probably have a case of similar organisation and en- 

 vironment determining the same instinct ; for the latter 



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