BY THE GENERAL SURFACE OF THE SKIN. 207 



act directly on the cephalic ganglia, Graber decapi- 

 tated a certain number, and found that the light still 

 acted on them in the same manner, though the dafiier- 

 ences were not so marked. He also covered over the 

 eyes of newts, and found that the same held good with 

 them. 



Hence he concludes that the general surface of the 

 skin is sensitive to light. These results are certainly 

 curious and interesting, but even if we admit the 

 absolute correctness of his deductions, I do not see that 

 they are in opposition to those at which I had arrived. 

 My main conclusions were that ants, Daphnias, etc., 

 were able to perceive light of different wave-lengths, 

 and that their eyes were sensitive to the ultra-violet 

 rays much beyond our limits of vision. His observa- 

 tions do not in any way controvert these deductions; 

 indeed, the argument by which he endeavours to prove 

 that the effect is due to true light, and not to warmth, 

 presupposes that sensations which can be felt by the 

 general surface of the skin, would be still more vividly 

 perceived by the special organs of vision. 



In connection with this subject, I may add that I do 

 not at all doubt the sensitiveness to light of eyeless 

 animals. In experimenting on this subject, I have 

 always found that though the blind woodlice (Platy- 

 arthrus), which live with the ants, have no eyes, yet if 

 part of the nest be uncovered and part kept dark, 

 they soon find their way into the shaded part. It is, 

 however, easy to imagine that in unpigmented animals, 

 whose skins are more or less semi-transparent, the 

 light might act directly on the nervous system, even 

 though it could not produce anything which could be 

 called vision. 



