376 SIR J. LUBBOCK ON ANTS, BEES, AND WASPS. 



I then tried similar experiments with a saturated solution of 

 chrome alum and chromium chloride. These are dark greenish 

 blue, very opaque to the visible light-rays, but transparent to the 

 ultra-violet. I used a layer J inch thick, which was still so dark 

 that I could not see the ants through it ; and for comparison, a 

 solution 1 inch thick of bisulphide of carbon, moving them after 

 each observation as before. 



Exp. 1. The ants were under the bisulphide of carbon. 

 o 



5> '"• 5J ?) » 



„ 3. Most „ „ „ 



„ 4. All but three „ „ „ 



„ 5. All „ „ „ 



I now took chromium chloride instead of chrome alum. 

 Exp. 1. Most were under the bisulphide of carbon. 



„ 2. All „ „ „ 



„ 3. Almost all „ „ „ 



„ 4. About three fourths were under the chromium 

 chloride. 



„ 5. All were under the chromium chloride. 



„ 6. About two thirds „ „ 



„ 7. About one half under each. 



„ 8. All under the bisulphide of carbon. 



„ 9. About three fourths under the bisulphide of carbon. 



„ 10. About half „ „ „ 



„ 11. All under the chrome alum. 



„ 12. „ bisulphide of carbon. 



Thus, then, while if the ants have to choose between the violet 

 and other coloured glasses, they will always prefer one of the 

 latter, the effect of putting over the violet glass a layer either of 

 sulphate of quinine or bisulphide of carbon, both of which are 

 quite transparent, but both of which cut off the ultra-violet rays, 

 is to make the violet glass seem to the ants as good a shelter as 

 any of the other glasses. This seems to me strong evidence that 

 the ultra-violet rays are visible to the ants. 



Prof. Paul Bert has made ('Archiv de Physiol.' 1869, p. 547) 

 some very interesting experiments on a small freshwater Crusta- 

 cean belonging to the genus Daphnia, from which he concludes 

 that they perceive all the colours known to us, being, however, 

 specially sensitive to the yellow and green, and that their limits 

 of vision are the same as ours. 



Nay, he even goes further than this, and feels justified in con- 



