HAMLIN ON THE SALMON OF MAINE. 345 



easily distinguished. The first river has a race of well-shaped salmon 

 whose average weight is about ten pounds. The second has a strong, 

 coarse-scaled, rather long but very hardy salmon, whose average weight, 

 is about seventeen pounds. The third river has a middling-shaped 

 salmon, whose average weight is about nine pounds. The fourth river 

 has a long, ill-shaped salmon, averaging about eight pounds; and the 

 fifth river has a very well-shaped salmon, whose average weight is full 

 fourteen pounds." This experienced naturalist adds that it is rare for 

 a salmon returning through the common estuary to miss its way to its 

 own stream. 



The difference of proportions in salmon taken from different and even 

 contiguous rivers has often been noticed, and is due to local causes. 

 The proportions between the salmon of the river Bush and the river 

 Bann near the Giant's Causeway differ in the ratio of length to girth 

 as 20 to 9 and 20 to 13. 



The differences of color between the lake and migratory salmon are 

 not great, and Agassiz does not regard color as of any importance in 

 relation to specific character. The sea-salmon, when well-fed, has a 

 smaller head, a more rounded body, and a more silvery luster. The 

 small heads and rounded bodies, considered as merely proportional, are 

 easily explained by the influence of food. The colorings of the fish are 

 dependent upon the same cause, as well as upon age, season, and the 

 purity and chemical composition of the water they frequent. For effect 

 of food and locality we have many positive examples among our do- 

 mestic animals and birds. Thus the lake-salmon may be identical with 

 the migratory salmon, altered in size and disposition after many gen- 

 erations. This principle of change of character and transmission of such 

 character to offspring is well explained by Darwin. 



If there is no difference in typical structure, there is, however, a 

 marked discrepancy in the habits of the two fishes, for the one has lost 

 the instinct to visit the sea ; and this is a very marked characteristic 

 with the migratory salmon, the young fish sometimes throwing them- 

 selves upon the shore in their frantic endeavors to pass the barrier- 

 dams. However, the English naturalists have admitted that it was 

 possible for the parr to lose its instinct for the sea and propagate its 

 species in the rivers, deteriorating greatly in size and quality. 



The sea trout, Salmo trutta, can breed and thrive quite well without 

 descending to the sea, but it soon loses its marked characteristics, and 

 resembles the common trout. 



All of the systems of lakes where the fresh-water salmon is found 

 were frequented by the sea-salmon up to within a comparatively short 

 period of time, and the dams of the mill-men are now the only barriers 

 to the migration and emigration of the fish. We can readily conceive 

 that the young salmon might remain over one or two seasons in these 

 lakes before visiting the sea, propagating a family which had less de- 

 sire to visit the salt water ; and thus in successive generations a race 



