CLASSIFICATION AND THE PREDICABLES. 175 



necessary to remark, that a species, even as referred 

 to the same genus, will not always have the same 

 differentia, but a different one, according to the prin- 

 ciple and purpose which presides over the particular 

 classification. For example, a naturalist surveys the 

 various kinds of animals, and looks out for the classi- 

 fication of them most in accordance with the order in 

 which, for zoological purposes, it is desirable that his 

 ideas should arrange themselves. With this view he 

 finds it advisable that one of his fundamental divisions 

 should be into warm-blooded and cold-blooded animals ; 

 or into animals which breathe with lungs and those 

 which breathe with gills ; or into carnivorous, and 

 frugivorous or graminivorous; or into those which 

 walk on the flat part and those which walk on the 

 extremity of the foot, a distinction on which some of 

 Cuvier's families are founded. In doing this, the 

 naturalist creates as many new classes, which are by 

 no means those to which the individual animal is fami- 

 liarly and spontaneously referred ; nor should we ever 

 think of assigning to them so prominent a position in 

 our arrangement of the animal kingdom, unless for a 

 preconcerted purpose of scientific convenience. And 

 to the liberty of doing this there is no limit. In the 

 examples we have given, the new classes are real 

 Kinds, since each of the peculiarities is an index to a 

 multitude of properties belonging to the class which 

 it characterizes : but even if the case were otherwise 

 if the other properties of those classes could all be 

 derived, by any process known to us, from the one 

 peculiarity on which the class is founded even then, 

 if those derivative properties were of primary import- 

 ance for the purposes of the naturalist, he would be 

 warranted in founding his primary division upon 

 them. 



