THE SENSE OF COLOUR 29 



just as man sees it. This is a question which deserves 

 to be pursued further, but this is not the place to 

 pursue it. 



2. A Speculation. 



To set about discovering in what the difference (if it exists) 

 of sensitiveness to colour in the eye of the trout and the 

 eye of man consists, is an extremely difficult matter. I do 

 not profess the anatomical or optical knowledge which 

 would enable me to probe it scientifically. I do not 

 know whether the problem is or ever will be soluble, what- 

 ever be the scientific advance of man. I hope it may be 

 possible to solve it some day, if it be for the good of fly 

 fishing as an art. In the meanwhile I may perhaps be 

 forgiven some empirical speculations in the direction of a 

 solution, some gropings after the truth. 



It may, I think, be taken as a starting-point that, 

 whatever be the nature of the trout's faculties of vision, 

 they are designed to subserve his earning his living and 

 the preservation of his species. 



One starts by observing that in weedy rivers trout live 

 in an environment of green; in gravelly or rocky rivers 

 they live in an environment of brown. One knows from 

 the attractiveness of the Red Tag and the Zulu that they 

 are peculiarly sensitive to red. 



In their food one finds among the duns a prevalence 

 of greens and yellows; among the sedges reds, orange, 

 and brown ; in the Perlidae, or willow flies, browns ; and in 

 the alder brown and plum colour. There is not, however, 

 except very faint in the wings of duns, any great quantity 

 of blue in the food of trout, nor does it prevail in their 

 habitat, except in combination with yellow to make 

 green. I am not forgetting the iron-blue dun. That is 

 easily to be picked out as a very dark fly against the light, 



