PARTS OF ANIMALS, III. i. 



front teeth contribute a great deal to the formation 

 of the sounds. 



As we have said, the teeth of some of the animals 

 have one function only, to break up the food. Of 

 those animals whose teeth serve also as a defence 

 and as weapons, some (like the SA\ine) have tusks, 

 some have sharp interlocking teeth, and are called 

 " saw-toothed " as a result. The strength of these 

 latter animals lies in their teeth, and sharpness is 

 the means of securing this ; so the teeth which are 

 serviceable as weapons are arranged to fit in side by 

 side when the jaws are closed to prevent them from 

 rubbing against each other and becoming blunt. No 

 animal has saw-teeth as well as tusks ; for Nature 

 never does anything without purpose or makes any- 

 thing superfluously. These teeth are used in self- 

 defence by biting ; tusks by striking. This explains 

 why sows bite : they have no tusks. 



(At this point we should make a generalization, "The more 

 which will help us both in our study of the foregoing J-^^^ F^^ 

 cases and of many that are to follow. Nature allots 

 defensive and offensive organs only to those creatures 

 which can make use of them, or allots them " in a 

 greater degree," " and " in the greatest degree " to 

 the animal which can use them to the greatest ex- 

 tent. This applies to stings, spurs, horns, tusks, and 

 the rest. Example : Males are stronger than females 

 and more spirited ; hence sometimes the male of a 

 species has one of these parts and the female has 

 none, sometimes the male has it "in a greater degree." 

 Parts which are necessary for the female as well as 

 for the male, as for instance those needed for feed- 

 ing, are of course present though " in a less degree " ; 

 but those which serve no necessary end are not 



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