ON THE SENSITIVENESS OF THE SKIN TO LIGHT. 405 



were that ants, Daphnias, &c., 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 observations do not in any 

 way controvert these deductions : indeed the argument 

 by which (p. 234) he endeavours to prove that the 

 effect is due to true light and not to warmth, pre- 

 supposes that sensations which can be felt by the 

 general surface of the skin are still more vividly 

 perceived by the special organs of vision. 



Professor Graber's observations have been followed 

 up by M. Forel.^ He took fifteen specimens of Camp- 

 onotus ligniperdus, which is a large species, and, 

 moreover, possesses the advantage, for this purpose, 

 of having no ocelli, and carefully covered thp eyes 

 with opaque varnish. He then placed them in a box 

 with ten normal specimens of the same species (to 

 which he subsequently added five more), and covered 

 over one half of the box with cardboard and the other 

 half with a layer of water. In this way the one half 

 of the box was darker than the other, but the tempera- 

 ture of the two sides was approximately equal. In 

 four experiments the numbers were as follows : — 



Undee the Cakdboard. Under the Water. 



28 33 32 



It will be seen that a very large majority of the 

 normal ants in every case went under the cardboard; 

 while it was practically indifferent to the hoodwinked 



' Beo. Zool. Suisse, 1887. 



