204 PERCEPTION OF LIGHT 



though apparently identical to us, appeared to the ants 

 very different, and that, as before, they preferred to 

 rest under the liquid which intercepted the ultra-violet 

 rays. In two or three cases only they went under the 

 other bottle ; but I ought to add that my observations 

 were made in winter, when the ants were rather 

 sluggish. I am disposed to think that in summer 

 perhaps these exceptional cases would not have 

 occurred. 



Professor Graber, however, while admitting the 

 accuracy of my observations, has attempted to prove 

 that the perception of the ultra-violet rays is not a 

 case of sight in the ordinary acceptation of the words, 

 but is due to the general sensitiveness of the skin. 



It has long been known that some of the lower 

 animals which do not possess eyes are, nevertheless, 

 sensitive to light. Hoffmeister,* in his work on earth- 

 w^orms, states that, with some exceptions, they are 

 very sensitive to light. Darwin, perhaps, experimented 

 with a different species (for there are many different 

 kinds) ; at any rate, his specimens seemed to be less 

 keenly affected, though if one was suddenly illumi- 

 nated it dashed "like a rabbit into its burrow." He 

 observed, how^ever, that some individuals were more 

 sensitive to light than others, and that the same indi- 

 viduals by no means always acted in the same way. 

 Moreover, if they " were employed in dragging leaves 

 into their burrows or in eating them, and CA^en during 

 the short intervals when they rested from their work, 

 they either did not perceive the light or were regard- 

 less of it."t He observes, however, that it is only the 



* " Familie der Eegenwiirmcr," IS45. 

 t Dar.viu's ''Earthworms." 



