20 THE rfENSE OF COLOUR. 



ne trouvons-nous pas la une raison de plus pour 

 supposer que le role des milieux de 1'oeil est tout-a-fait 

 secondaire, et que la visibilite tient a 1'impressionnabilite 

 de 1'appareil nerveux lui-meme ? ' 



Such a generalisation would seem to rest on but a 

 slight foundation ; and I may add that I have made 

 some experiments myself 1 on Daphnias which do not 

 agree with those of M. Bert. On the contrary, I 

 believe that the eyes of Daphnias are in this respect 

 constituted like those of ants. 



These experiments seem to me very interesting. 

 They appear to prove that ants perceive the ultra-violet 

 rays. Now, as every ray of homogeneous light which 

 we can perceive at all appears to us as a distinct colour, 

 it becomes probable that these ultra-violet rays must 

 make themselves apparent to the ants as a distinct 

 and separate colour (of which we can form no idea), 

 but as unlike the rest as red is from yellow, or green 

 from violet. The question also arises whether white 

 light to these insects would differ from our white light 

 in containing this additional colour. At any rate, as 

 few of the colours in nature are pure, but almost all 

 arise from the combination of rays of different wave- 

 lengths, and as in such cases the visible resultant would 

 be composed not only of the rays which we see, but of 

 these and the ultra-violet, it would appear that the 

 colours of objects and the general aspect of nature 



1 British Atsoc. Report 1881, and Linnean Soc. Jotirn. 1882. 



