150 A PHILOSOPHER WITH NATURE 



to cover them, fish of two pounds, of five pounds, of 

 ten pounds, meeting their mates, scratching in the 

 gravel, depositing their spawn. And then returning 

 once more, spent and exhausted, to the sea. 



What is the real explanation of this instinct which 

 drives the sea trout, like the salmon, thus to return 

 from their sea-going life to spawn, not merely in fresh 

 water and in running streams, but in particular 

 places and in quite shallow water, often of a few 

 inches ? It is interesting to note in most hatcheries 

 how extremely significant are the conditions under 

 which the eggs of salmon trout and salmon have 

 to be hatched out. The eel returns from inland 

 waters to spawn in the depths of the ocean. 

 Probably considerable pressure is necessary to its 

 eggs, as it is to the eggs of many sea fishes, before 

 they will hatch out. In the case of the migratory 

 trout the fact which probably determines the curious 

 life-history of the fish is the very interesting, 

 although withal very simple one, connected with 

 the eggs. The eggs of the trout will not hatch out 

 in any but the shallowest water. The least pressure 

 is quite fatal to them. This is a fact well known at 

 all artificial hatcheries, and all arrangements have to 

 be made accordingly. It was no doubt around this 

 little tuft of circumstance that the strange and 

 eventful history of the salmon family slowly evolved 

 itself. When the trout took to migrating to the 

 sea or the river estuaries at first there probably was 

 no universal instinct to return to their old haunts 

 for spawning purposes. For ages there must have 

 been, as indeed there may be now, salmon trout 

 tending to shed their spawn where they lived, in the 

 rivers, in the estuaries, in the seas. But in the 



