THEORY OF COLOUR. 109 



taken, probably, from some very bright and sunny water. In 

 this view I am fully sustained by Professor Agassiz, who has 

 made some very curious experiments with regard to the colours 

 of fishes, of the Salmonid(B especially ; and who has ascertained, 

 beyond a doubt, not only that the Trout of diiferent neigh- 

 bouring waters are affected by the colour and quality of the 

 water, but that the Trout of the same river vary in colour 

 accordingly as they haunt the shady or the sunny side of the 

 stream. For it is a well-known fact, that the Salmonida, 

 although many of them are migratory at certain seasons, have 

 their own haunts and hunting-grounds to which they steadily 

 adhere, moving but a short distance from one spot, in pursuit 

 of their prey, and returning to it when satisfied. 



Thus, in a mountain-brook, you shall find, perhaps, that the 

 pool between an upper and lower fall or rapid is occupied by 

 two fish ; one of these will lie at the head, the other at the tail, 

 of the pool, the more powerful fish selecting the spot which he 

 chooses, and neither exchanging places, nor hunting far from 

 his habitual haunts. 



In still waters, in like manner, you will find that, day after 

 day, the same large Trout will be seen under this bank, by that 

 large stone, or in the cavity formed by the roots of yon ash or 

 alder ; and that he will not stray to any distance from it, but 

 will seek his prey nearly in the same waters, and on the same 

 side of the river, the opposite bank being probably held by a 

 rival fish. 



That this will at first be deemed far-fetched and improbable, 

 I think likely enough ; but the more we consider it, the more 

 reasonable shall it appear ; for when we weigh the great influence 



