224 THE THEORIES OF EVOLUTION 



straightened-out shells. Le Dantec is certainly mis- 

 taken, for Hyatt in his description of the degenerated 

 shells says that they become deformed, smaller and 

 smoother, that their coils assume a more cylindrical 

 shape and that their impressed zone disappears. 9 

 Hyatt mentions somewhere the absolute similarity be- 

 tween the degenerate adult shells and the original 

 straight shells, which excludes the existence of an im- 

 pressed zone in the former. 



Our last example will illustrate the effects of use 

 and disuse of organs. Cattaneo made a study of ani- 

 mals which for countless ages have been domesticated, 

 horses and camels, and he suggested, after BufFon, 

 that the camel's humps and the callouses on their knees 

 were due to the loads that are placed on their backs 

 and to the kneeling attitude they are made to assume 

 while being loaded. He mentions that the famous 

 traveller Prjevalsky killed in Central Asia two wild 

 camels or rather two camels having reverted to the 

 wild state, which had no callouses and whose humps 

 were twice as small as the normal ones. Humps and 

 callouses are, as we know, hereditary in camels and are 

 not acquired by every new generation. 



Another author, Ritter, described upon the authority 

 of a Turkish geographer of the seventeenth century, 

 camels having run wild and whose humps were hardly 

 noticeable. Certain drawings from Nineveh and 



» A. Hyatt, loc. cit., p. 337. 



