PROGRESSION OF ANIMALS, xvi.-xvii. 



them, live in holes ; for creatures that live thus 

 cannot be tall. 



Crabs are the most strangely constituted of all the 

 polypods ; for they do not progress forward (except 

 in the sense already mentioned"), and they alone 

 among animals have several leading legs.^ The 

 reason is the hardness of their feet and the fact that 

 they use them not for swimming but for walking ; 

 for they always go along the ground." All the 

 polypods bend their legs obliquely like the quad- 

 rupeds that live in holes ; lizards, for instance, and 

 crocodiles and most oviparous quadrupeds are of 

 this nature. The reason is that they live in holes, 

 some only during the breeding season, others through- 

 out their lives. 



XVII. Now the other polypods '^ are bow-legged 

 because they are soft-skinned, but the legs of the 

 spiny lobster,^ which is hard-skinned, are used for 

 swimming and not for walking.^ The bendings of 

 crabs' legs are oblique but their legs are not bowed, 

 as are those of vivipai'ous quadrupeds and bloodless 

 polypods, because their legs are hard-skinned and 

 testaceous, the crab not being a SAvimming animal 

 and living in holes, for it lives on the ground. More- 

 over, the crab is round in shape and does not possess 

 a tail like the spiny lobster ; for the latter 's tail is 

 useful for swimming, but the crab does not swim. 

 And it is the only animal in which the side is like a 

 hinder part, because its leading feet are numerous,' 



' There is no single word in English for this animal, the 

 Latin locusta and the French langouste. 



f And therefore are not bowed, as Mich, explains. 



» Since the crab moves sidewise, one of its sides becomes 

 as it were the back, but why it should be so for the reason 

 given is obscure. 



537 



