PARTS OF ANIMALS, III. i. 



brought all these functions together under one part, 

 whose formation she varies in the different species to 

 suit its various duties. That is why the animals 

 which use their mouths for feeding, respiration and 

 speaking have rather narrow mouths, while those 

 that use them for self-defence have wide and gaping 

 mouths. All the saw-toothed creatures have these 

 wide mouths, for their method of attack is biting, and 

 therefore they find it an advantage to have a mouth 

 that will open wide ; and the wider it opens the 

 greater the space the bite will enclose, and the 

 greater the number of teeth brought into action. 

 Biting and carnivorous fishes have mouths of this 

 sort ; in the non-carnivorous ones it is on a tapering 

 snout, and this suits their habits, whereas a gaping 

 mouth would be useless. 



In birds, the mouth appears in the form of a beak, Beak, 

 which serves them instead of lips and teeth. Various 

 sorts of beak are found, to suit the various uses in- 

 cluding defensive purposes to which it is put. All 

 of the birds known as crook-taloned have a curved 

 beak, because they feed on flesh and take no vegetable 

 food : a beak of this form is useful to them in master- 

 ing their prey, as being more adapted for the exertion 

 of force. Their beak, then, is one weapon of offence, ^ 

 and their claws are another ; that is why their claws 

 are exceptionally curved. Every bird has a beak 

 which is ser\-iceable for its particular mode of life. 

 The woodpeckers, for instance, have a strong, hard 

 beak ; so have crows, and other birds closely related 

 to them ; small birds, on the other hand, have 

 a finely constructed beak, for picking up seeds and 

 catching minute animals. Birds that feed on herb- 

 age and that live by marshes (e.g. swimmers and 



215 



