152 A PHILOSOPHER WITH NATURE 



banks which run east and west rather than north and 

 south. 



We may see also why it is that the salmon trout 

 which the angler meets like the salmon in certain 

 waters in certain seasons has reached the place 

 where he is found at that particular time. The 

 eggs of his mate will hatch out only in water at a 

 temperature not high above freezing-point. All the 

 flit tings of the fish must therefore be arranged so 

 that he may arrive at the spawning-ground in the 

 colder months of the year, according to locality. 

 Others may suit their journey to more convenient 

 seasons ; for him it is expedient that his flight should 

 be in winter. It is probably for a similar reason 

 that we find many of the movements of salmon so 

 puzzling. It has often been pointed out that it 

 cannot be simply in obedience to the sexual instinct 

 that the salmon ascends the rivers, for many of the 

 fish have little development of roe when they leave 

 the sea. But when the object is kept in mind, it is 

 all quite clear. Some of the fish ascend rivers to 

 spawn which are but a few miles long, while others 

 have to travel to their destination for hundreds of 

 miles. In all cases the spawning time of the salmon, 

 like the sea trout, is in the same months of the winter, 

 so that the journeys which it undertakes must be 

 arranged accordingly. 



