58 iii. I. 



case the animal is said to be saw-toothed. The explanation of 

 this latter arrangement is as follows. The strength of such an 

 animal is in its teeth, and the efficacy of these depends on their 

 sharpness. In order, then, to prevent their getting blunted by 

 mutual friction, such of them as serve for weapons fit into each 

 other's interspaces, and are so kept in proper condition. No 

 animal that is saw-toothed is at the same time furnished with 

 tusks.3 For nature never makes anything superfluous or in vain. 

 She gives, therefore, tusks to such animals as strike in fighting, 

 and serrated teeth to such as bite. Sows, for instance, have no 

 tusks, and accordingly sows bite instead of striking. 



A general principle must here be noted, which will be found 

 applicable not only in this instance but in many others that will 

 occur later on. Nature allots each weapon, offensive or defensive, 

 to those animals alone that- can use it; or, if not to them alone, 

 to them in a more marked degree ; and she allots it in its most 

 perfect state to those that can use it best ; and this whether it 

 be a sting, or a spur, or horns, or tusks, or what it may of a like 

 kind. 



Thus as males are stronger and more choleric than females, 

 It is in males alone that such parts as those just mentioned are 

 found, or at any rate it is in males that they are found in the 

 highest degree of perfection.* For though females are of course 

 provided with such parts as are no less necessary to them than 

 to males, the parts for instance which subserve nutrition, they 

 have even these in an inferior degree,^ and the parts which answer 

 no such necessary purpose they do not possess at all. This 

 explains why stags have horns, while does have none ; why the 

 horns of cows are different from those of bulls, and, similarly, 

 the horns of ewes from those of rams. It explains also why the 

 females are often without spurs in species where the males are 

 provided with them, and accounts for similar facts relating to 

 other such parts.^ 



All fishes have teeth of the serrated form, with the single 

 exception of the fish known as the Scarus.' In many of them 

 there are teeth even on the tongue and on the roof of the mouth.^ 

 The reason for this is that, living as they do in the water, they 

 cannot but allow this fluid to pass into the mouth with the food. 

 The fluid, thus admitted, they must necessarily discharge again 

 without delay. For were they not to do so, but to retain it for 

 662 a. 



