ORIGIN OF LAKE SALMON. 141 



stocked with salmon and smelts. If both of these fish had formerly been more generally 

 distributed, in view of the fact just stated, it is hard to conceive of any reason for their 

 disappearance from waters which evidently were perfectly well adapted to their con- 

 tinued existence. Furthermore, there has never been any evident attempt of transplanted 

 lake salmon and smelts to go to sea. The occasional occurrence of both young and adults 

 in outlets is plainly explainable on other grounds. 



Atkins beUeved that the fresh-water salmon was derived from the sea salmon, and 

 suggested that it was possible that the change in their habits and instincts occurred 

 gradually. Doubtless that is a fact, and a theory once suggested to me, was that the 

 'land-locking' of the sea salmon was a voluntary process on the part of the salmon, and 

 that conditions satisfactory to the salmon, particularly those of food supply and water 

 temperature, were the principal factors concerned. The considerable individual varia- 

 tions of salmon in the same lake were accounted for by assuming that the 'land-locking' 

 process had continued for a very long period, even from the time that the salmon first 

 ascended into those waters. Those adult individuals, which exhibited the most pro- 

 nounced differences from the sea salmon were supposed to be descendants of the earUest 

 individuals to breed in those waters. It was assumed that as long as the sea salmon had 

 access to the lakes, there were some of the offsprings which annually remained and 

 matured there. A part of these interbred with the older inhabitants, a portion bred 

 with contemporary broods, and others perhaps, interbred with matured offsprings of 

 subsequent additions from the sea salmon runs, etc. 



This idea was supposed to account for the fact that there were individual lake salmon 

 so markedly different from the sea salmon that they could consistently be regarded as 

 distinct species, while others were hard to distinguish. While to some extent satisfying 

 the requirements of explanation, this theory possessed one serious defect in that it did 

 not explain why all of the old strain and all of the subsequent crosses remained in fresh 

 water, while only the broods of the pure strain of sea salmon went to sea, which it seems 

 must have been the case, for the sea salmon never appear to show any similar individual 

 variations when fresh from the sea. 



If none of the theories that have been advanced are tenable, what can be offered as an 

 excuse for the existence of the so-called landlocked salmon or lake salmon? It seems 

 to me that the question can be answered with some degree of plausibiUty by adopting 

 some of the ideas expressed in our previous discussion concerning the evolution of the 

 Salmonidae. However, it should be said that without further research such an answer 

 is of necessity fully as theoretical as any of the foregoing, but it appears to me to afford 

 fewer vulnerable points. Such a theory differs in but few essentials from that of the 

 voluntary landlocking process just mentioned. Thus instead of the lake salmon being 

 merely the sea salmon, which, as Dr. Hamlin's (1874, p. 341) Indian guide said, 'forgot 

 to go to sea,' it is a divergent from a common ancestral or primitive stock, as Goode 

 says. But this primitive stock was a marine, not a fresh-water fish. 



One conceivable way to account for the divergence of the lake salmon and its adapta- 

 tion to fresh water is that the divergence culminated since the last glacial period. It is 



