PARTS OF ANIMALS, IV. xii. 



bird that has talons and can fly well : spurs are useful 

 for fights on the ground, and that is why certain of 

 the heavy birds possess them, while talons would not 

 be merely useless to them but a real disadvantage " : 

 they would stick in the ground and impede the birds 

 when walking. And in fact all crook-taloned birds 

 do walk badly, and they never perch upon rocks ; 

 in both instances the nature of their claws is the 

 impediment.** 



This state of affairs is the necessary result of the 

 process of their development. There is earthy sub- 

 stance in the bird's body which courses along and 

 issues out and turns into parts that are useful for 

 weapons of offence. When it courses upwards it 

 produces a good hard beak, or a large one ; if it 

 courses downwards it produces spurs on the legs or 

 makes the claws on the feet large and strong. But 

 it does not produce spurs and large claws simul- 

 taneously, for this residual substance would be 

 weakened if it were scattered about. Again, some- 

 times this substance makes the legs long ; and in 

 some birds, instead of that, it fills in the spaces be- 

 tAveen the toes. Thus it is of necessity that water- 

 birds either are web-footed, simply, or (if they have 

 separate toes) they have a continuous fan or blade, 

 as it were, running the whole length of each toe and 

 of a piece with it. 



From the reasons just stated it is clear that feet 

 of this sort are the result of necessity, it is true ; but 

 they conduce to a good end and are meant to assist 

 the birds in their daily life, for these birds hve in the 

 water, and Avhile their wings are useless to them, 

 these feet are useful and help them to swim. They 



" See above, note on 648 a 16. 



ο 411 



