196 GOLDEN DAYS 



of the stream, it would actually suggest 

 the prismatic likeness of a particular 

 species as the trout know it. 



The recent controversy as to colour- 

 blindness in fish does not really matter, 

 because we know that each colour has its 

 own particular tone-value. It is im- 

 material, therefore, whether the eye of 

 a fish registers colour, or what we under- 

 stand as colour, so long as it discriminates 

 between the different tonalities of various 

 tints. 



Can this idea be amplified by means of 

 an artificial Mayfly ? Let us suppose we 

 dress it with wings of the brightest emerald 

 green, and body of cerulean blue, ribbed 

 with lemon yellow. The result, of course, 

 would appeal to the instincts of a sophisti- 

 cated trout as little as to those of the 

 exquisite purist. Both would remain 

 calmly contemptuous, and yet we have 

 taken trouble over our little fly. His 

 form and proportions are correct and life- 

 like, but the trout (the purist has rushed 

 off to contemplate a " pale watery dun ") 

 takes not the slightest notice. We may 

 put our fly over the feeding fish again and 



