404 COLOUR-SENSE OF ANTS. 



sensitive to the ultra-violet rays, by similar observa- 

 tions on earthworms, newts, &c. It is interesting, 

 moreover, that the species examined by him showed 

 themselves, like the ants, especially sensitive to the 

 blue, violet, and ultra-violet rays. Professor Graber, 

 however, states that he differs from me, inasmuch as I 

 attributed the sensitiveness to the ultra-violet rays 

 exclusively to vision ; that it is * ausschliesslich durch 

 die Augen vermittelt.' I would not, however, express 

 that opinion as applying absolutely to all animals, 

 though it is, I believe, true of ants, where the opacity 

 of the chitine renders it unlikely that the light would 

 be perceived except by the medium of the eyes and 

 ocelli. 



Graber has demonstrated in earthworms and newts, 

 and Plateau in certain Myriapods, ^ that these animals 

 perceive the difference between light and darkness by 

 the general surface of the skin. But, more than this, 

 Graber appears to have demonstrated that earthworms 

 and newts distinguish not only between light of different 

 intensities, but also between rays of different wave- 

 lengths, preferring red to blue or green, and green to 

 blue. He found, moreover, as I did, that they are 

 sensitive to the ultra-violet rays. Earthworms, of 

 course, have no eyes ; but thinking that the light might 

 perhaps act directly on the cephalic ganglia, Graber 

 decapitated a certain number, and found that the light 

 still acted on them in the same manner, though the 

 differences 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 



' /(WWW. de VAnatomie et de la Physiohgie, 1886, p. 431. 



