PROGRESSION OF ANIMALS, xvii.-xviir. 



The reason is that it does not bend its legs forwards 

 and is not bow-legged. Why it is not bow-legged 

 has been already explained before, namely, because 

 its skin is hard and testaceous. For this reason it 

 must lead off with all its legs and obliquely — obliquely 

 because its bendings are oblique, and \vith all its legs, 

 because otherwise those Avhich were at rest would 

 impede those which Λvere moving. 



Flat-fish sAvim as one-eyed men walk ; for their 

 nature is distorted. Web-footed birds swim with 

 their feet. They are bipeds, because they take in 

 breath and respire ; they are web-footed, because 

 they live in the water, for their feet being of this 

 kind are of service to them in place of fins. They do 

 not have their legs, as the other birds do, in the 

 centre of the body, but placed rather towards the 

 back ; for since they are short-legged, their legs 

 being set back are useful for SAvimming. This class 

 of bird is short-legged because nature has taken 

 away from the length of their legs and added to their 

 feet, and has given thickness instead of length to 

 the legs and breadth to the feet ; for, being broad, 

 they are more useful than if they were long, in order 

 to force aAvay the water when they are swimming. 



XVIII. It is for a good reason, too, that winged 

 animals have feet, while fishes have none. The 

 former live on dry land and cannot always remain up 

 in the air, and so necessarily have feet ; but fishes 

 live in the water, and take in water and not air. 

 Their fins, then, are useful for svdmming, Λvhereas 

 feet would be useless. Also, if they had both feet 

 and fins, they would be bloodless. Birds in a way 



^ ■TrXareis Ζ : τταχεΓ? PSUY. 



s 539 



