SEA TROUT 151 



nature of things no grain of it has ever come to 

 maturity. Only the fish which happened to return 

 to spawn to the shallow upland waters have ever 

 left any descendants. Hence the rigid process of 

 long-continued natural selection which evolved the 

 present habits of the salmon and which every year 

 drives all the existing members of the salmon family 

 to their spawning-grounds. Hence the imperative- 

 ness of the instinct to which they are subject. They 

 are, as it were, the survivors of a vast army which 

 must have become extinct through lack of the 

 instinct now developed in them. 



Salmon trout are persistent travellers within a 

 certain limited area. A fish of a few pounds weight 

 which rises to the fly of the angler has in all pro- 

 bability journeyed through the same waters before. 

 The salmon moves far in its migrations and even 

 goes far to sea, but the sea trout has a more local 

 range. For instance, a considerable proportion of 

 marked fish have been known to return to the same 

 small stream and to exactly the same locality the 

 year following that in which they were marked. It 

 is one of the most interesting features of the migra- 

 tion of salmon trout that large fish of several pounds 

 weight will ascend quite narrow rivulets for spawn- 

 ing purposes. If one may judge, indeed, by facts 

 obtained from artificial experiences, the conditions 

 which the fish seek for successful spawning are not 

 easy to find. Not only must the water be extremely 

 shallow and running, but the eggs cannot be hatched 

 out in strong light, nor wiU they come to maturity 

 except the water be kept at a low temperature. The 

 salmon trout, therefore, seem naturally to deposit 

 their eggs in dark or shaded situations and between 



