PARTS OF ANIMALS, IV. xii. 



are like oars to a sailor or fins to a fish. A fish that 

 has lost its fins can no longer swim ; nor can a bird 

 whose webs have been destroyed. 



Some birds have long legs, owing to their living in 

 marshes ; for Nature makes the organs to suit the 

 work they have to do, not the work to suit the organ. 

 And these birds have no webs in their feet because 

 they are not water birds, but because they live on 

 ground that gives under them they have long legs 

 and long toes, and most of them have additional joints 

 in their toes. Furthermore, though these birds are 

 not great fliers, they are composed of the same ma- 

 terials as the rest, and thus the nutriment which in the 

 others goes to produce the tail feathers, in these is 

 used up on the legs and makes them grow longer, and 

 Avhen in flight these birds stretch them out behind 

 and use them in place of the missing tail feathers : 

 placed thus, the legs are useful to them ; otherwise 

 they would get in the way. 



Short-legged birds keep their legs up against the 

 belly while they are flying, because if the feet are 

 there they are out of the way ; the crook-taloned 

 birds do it for an additional reason : the feet are 

 convenient for seizing prey. 



When a bird has a long neck, this is either thick and 

 is held stretched out during flight ; or it is slender 

 and is bent up during flight, because being protected 

 in this way it is less easily broken if the bird flies into 

 anything. All birds have an ischium, but in such 

 a way that they ΛνοηΜ not appear to have one ; it is 

 so long that it reaches to the middle of the belly and 

 looks more like a second thigh-bone. The reason for 

 this is that a bird, although a biped, does not stand 



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