122 THE EVOLUTIONIST AT LARGE. 



species is very sensitive to small points of 

 detail in its own kind, and that the choice 

 would only be exerted between mates gene- 

 rally very like one another, so that extremely 

 minute differences must necessarily turn the 

 scale in favour of one particular suitor rather 

 than his rivals. Anglers know that trout are 

 attracted by bright colours, that they can 

 distinguish the different flies upon which they 

 feed, and that artificial flies must accordingly 

 be made at least into a rough semblance 

 of the original insects. Some scientific 

 fishermen even insist that it is no use offer- 

 ing them a brown drake at the time of year 

 or the hour of day when they are naturally 

 expecting a red spinner. Of course their 

 sight is by no means so perfect as our own, 

 but it probably includes a fair idea of form, 

 and an acute perception of colour, while 

 there is every reason to believe that all the 

 trout family have a decided love of metallic 

 glitter, such as that of silver or of the sal- 

 mon's scales. Mr. Darwin has shown that the 



