BISULPHIDE OF CAEBON. 215 



I now took deep-red glass. 



1st obs. The ants were under the red glass. 



2nd „ Half of the ants were under each. 



3rd „ Most of the ants were under violet glass 



and bisulphide. 

 4th „ The ants were equally divided. 



It seemed evident, therefore, that while if violet 

 glass alone was placed side by side with red, yellow, or 

 green, the ants greatly preferred any of the latter, on 

 the other hand, if a layer of bisulphide of carbon, which 

 to our eyes is perfectly transparent, was placed over 

 the violet glass, they then went as readily, or even 

 more readily, under it than under other colours. 



In order to be sure that it was not the mere 

 presence of a fluid, or the two layers of glass, to which 

 this was due, I thought it would be well to try a similar 

 series of experiments, using, however, a layer of similar 

 thickness (1 inch) of water coloured light blue by 

 ammonio-sulphate of copper. 



I therefore took again the piece of violet glass, over 

 which I placed a flat-sided bottle, about I inch thick, 

 containing a light-blue solution of ammonio-sulphate 

 of copper ; and, in contrast with it, I used the same 

 coloured glasses as before. The difiference, however, 

 was very marked, the ants always preferring the red, 

 green, and yellow to the violet. 



These erperiments seem to demonstrate that in 

 the previous series the ants were really influenced by 



