220 THE SENSE OF COLOUR. 
ne trouvons-nous pas 14 une raison de plus pour 
supposer que le réle des milieux de l’wil est tout-a-fait 
secondaire, et que la visibilité tient a Vimpressionnabilité 
de Yappareil nerveux lui-méme ?’ 
Such a generalisation would seem to rest on but a 
slight foundation; and I may add that I have made 
some experiments myself! on Daphnias which de 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 Assoc. Report 1881, and Linnean Suc. Journ. 1882 
