198 The Outline of Science 



when it went out to sea, and whether it has spawned or not, and 

 more besides. 



Interpretation of the Salmon's Story 



When an animal frequents two different haunts, in one of 

 which it breeds, it is very often safe to say that the breeding- 

 place represents the original home. The flounder is quite com- 

 fortable far up the rivers, but it has to go to the shore-waters to 

 spawn, and there is no doubt that the flounder is a marine fish 

 which has recently learned to colonise the fresh waters. Its 

 relatives, like plaice and sole, are strictly marine. But it is im- 

 possible to make a dogma of the rule that the breeding-place 

 corresponds to the original home. Thus some kinds of bass, which 

 belong to the marine family of sea-perches, live in the sea or in 

 estuaries, while two have become permanent residents in fresh 

 water. Or, again, the members of the herring family are very 

 distinctively marine, but the shad, which belong to this family, 

 spawn in rivers and may spend their lives there. 



So there are two different ways of interpreting the life- 

 history of the salmon. Some authorities regard the salmon as a 

 marine fish which is establishing itself in fresh water. But others 

 read the story the other way and regard the salmon as a member 

 of a fresh-water race, that has taken to the sea for feeding 

 purposes. In regard to trout, we know that the ranks of those 

 in rivers and lakes are continually being reinforced by migrants 

 from the sea, and that some trout go down to the sea while others 

 remain in the freshwater. We know also in regard to a related 

 fish, the char, that while the great majority of kinds are now; 

 permanent residents in cold and deep, isolated northern lakes, 

 there are Arctic forms which live in the sea but enter the rivers to 

 spawn. These facts favour the view that the salmon was origi- 

 nally a marine fish. But there are arguments on both sides, and, 

 for our present purpose, the important fact is that the salmon is 

 conquering two haunts. Its evolution is going on. 



