SIB J. LTJBBOCK ON ANTS, BEES, AND WASPS. 369 



twice ; but the pupse were each time carried out of the magnesium- 

 light. 



These experiments seemed strongly to indicate, if not to prove, 

 that ants were really sensitive to the ultra-violet rays. Now to 

 these rays sulphate of quinine and bisulphide of carbon are ex- 

 tremely opaque, though perfectly transparent in the case of visible 

 rays, and therefore to our eyes entirely colourless and transpa- 

 rent. If, therefore, the ants were really affected by the ultra- 

 violet rays, then a cell containing a layer of sulphate of quinine or 

 bisulphide of carbon would tend to darken the underlying space to 

 their eyes, though to ours it would not do so. It will be remem- 

 bered that if an opaque substance is placed over a part of a glass 

 nest, other things being equal, the ants always congregate under 

 it ; and that if substances of different opacity are placed on dif- 

 ferent parts of a nest, they collect under that which seems to 

 them most opaque. 



Over one of my nests of Formica fusca, therefore, I placed two 

 pieces of dark-violet glass 4 inches by 2 inches ; and over one 

 of them I placed a cell containing a layer of bisulphide of 

 carbon, an inch thick, slightly coloured with iodine. In all 

 these experiments, when I moved the liquids or glasses, I gave 

 the advantage, if any, to the one under which experience showed 

 that the ants were least likely to congregate. The ants all 

 collected under the glass over which was the bisulphide of 

 carbon. 



I then thought that though no doubt the iodine rendered the 

 bisulphide more completely impervious to the ultra-violet rays, 

 I would try the effect of it when pure and perfectly colourless. 

 I therefore tried the same experiment with pure bisulphide, 

 moving the two glasses from time to time in such a manner that 

 the ants had to pass the first violet glass in order to reach that 

 over which was the bisulphide. 



At 8.30 the ants were all under the glass over which was the 

 bisulphide of carbon : I then changed the position. 

 8.45 ditto ditto ditto. 



9 ditto ditto ditto. 



9.15 ditto ditto ditto. 



Although the bisulphide of carbon is so perfectly transparent, 

 I then thought I would try it without the violet glass. I there- 

 fore covered part of the nest with violet glass, a part with a layer 



