PARTS OF ANIMALS, III. i. 



present. Thus, stags have horns, does have not. 

 Thus, too, cows' horns are different from bulls' horns, 

 and ewes' from rams'. In many species the males 

 have spurs while the females have not. And so with 

 the other such parts.) 



All fishes are saw-toothed except one species, 

 the Scarus.'* Many of them have teeth on their 

 tongues and in the roof of the mouth. This is 

 because as they live in the water they cannot help 

 letting some of it in as they take in their food, and 

 they have to get it out again as quickly as possible. 

 If they failed to do so, and spent time grinding the 

 food small, the water would run down into their gut. 

 So all their teeth are sharp and intended only for cut- 

 ting up the food. Further, they are numerous and 

 placed all over the mouth ; so by reason of their 

 multitude they can reduce the food into tiny pieces, 

 and this takes the place of the grinding process. 

 They are also curved ; this is because practically the 

 whole of a fish's offensive force is concentrated in 

 its teeth. 



The mouth, too, is present in animals on purpose Mouth, 

 to fulfil these same offices, but it has also a further 

 purpose, at any rate in those animals which breathe 

 and are cooled from without — namely, to effect re- 

 spiration. As we said earlier. Nature will often quite 

 spontaneously take some part that is common to all 

 animals and press it into service for some specialized 

 purpose. Thus, the mouth is common to all animals, 

 and its normal and universal function has to do with 

 food : but sometimes it has an extra function, peculiar 

 to some species only : in some it is a weapon, in others 

 a means of speech ; or more generally, though not 

 universally, it serves for respiration. Nature has 



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