PARTS OF ANIMALS, I. iii. 



privation, can admit no differentiation ; there cannot 

 be species of what is not there at all, e.g. of " foot- 

 less " or " featherless," ^ as there can be of " footed " 

 and " feathered " ; and a generic differentia must 

 contain species, else it is specific not generic. How- 

 ever, some of the differentiae are truly generic and 

 contain species, for instance " feathered " (some 

 feathers are barbed, some unbarbed) ; and likewise 

 " footed " (some feet are " many-cloven," some 

 " twy-cloven," as in the animals with bifid hoofs, 

 and some '* uncloven " or " undi\ided," as in the 

 animals with solid hoofs). Now it is difficult enough 

 to arrange the various animals under such hnes of 

 diflPerentiation as these, which after all do contain 

 species, in such a way that every animal is included in 

 them, but not the same animal in more than one of 

 them (e.g. when an animal is both Avinged and wing- 

 less, as ants, glow-worms, and some other creatures 

 are) ; but it is excessively difficult and in fact im- 

 possible to arrange them under the opposite lines of 

 differentiation. Every differentia must, of course, be- 

 long to some species ; and this statement wall apply 

 to the negative differentiae as well as to the positive. 

 Now it is impossible for any essential characteristic 

 to belong to animals that are specifically different and 

 at the same time to be itself one and indivisible ^ : it 

 ^'V'ill always admit of differentiation. (For example, 

 Man and Bird are both two-footed, but this essential 

 characteristic is not the same in both : it is differenti- 

 ated.^ And if they are both " blooded," the blood 

 must be different, or else it cannot be reckoned as 

 part of their essence.) If that is so, then, the one 



* As the privative characteristic would have to be. 

 « See below, 693 b 2 ff . 



83. 



