40 CATEGOEIES OF CLASSIFICATION. 



that class being founded upon a particular mode 

 of execution of the plan characteristic of the Ver- 

 tebrates, while the order to which the Whales 

 belong depends upon their complication of struc- 

 ture, ae compared with other members of the 

 same class. 



We may therefore say that neither form nor 

 complication of structure distinguishes classes, 

 but simply the mode of execution of a plan. In 

 Vertebrates, for instance, how do we distinguish 

 the class of Mammalia from the other classes of 

 the type ? By the peculiar development of the 

 brain, by their breathing through lungs, by their 

 double circulation, by their bringing forth living 

 young and nursing them with milk. In this 

 class the beasts of prey form a distinct order, 

 superior to the Whales or the herbivorous ani- 

 mals, on account of the higher complication of 

 their structure ; and for the same reason we 

 place the Monkeys above them all. But among 

 the beasts of prey we distinguish the Bears, as a 

 family, from the family of Dogs, Wolves, and 

 Cats, on account of their different form, which 

 does not imply a difference either in the compli- 

 cation of their structure or in the mode of execu- 

 tion of their plan. 



