GRILSE 47 
scales of the fish as secondary and more or less 
accidental results of his visiting the sea and feeding 
there. We admit that he thrives surprisingly in 
the sea for a fresh water fish, but we know he can 
spawn only in fresh water, and ask how can he be 
« marine fish if he cannot propagate his species in 
the sea. Do we call the common eel a sea fish 
because it spawns in the sea? We call it the fresh 
water eel. Is the shad a fresh water fish because 
it spawns in rivers? In my view, the prevailing 
characteristics of the group of fishes to which the 
salmon belongs are those of marine fish of plastic 
nature, capable of much local variation both of 
appearance and habit, many of which enter fresh 
water freely. The fry exhibit a strong impulse to 
descend the rivers of their birth and to enter the 
sea; they do not develop into normal or healthy 
adults if they are retained forcibly, nor under usual 
conditions do they come to sexual maturity unless 
they have visited the sea. In some localities where 
great lakes occur a degenerate race becomes possible, 
but these land-locked salmon cannot be regarded as 
representatives of what the salmon used to be; 
they are not the fish through which evolution could 
proceed. It is quite possible that Brachymystaz, 
the large salmonid of the Siberian rivers and Lake 
Baikal, which viewed systematically comes between 
Salmo and Coregonus, may be a migratory fish 
which remains in fresh water for longer periods 
than our salmon, and which in its great size and 
full development differs in this respect from the so- 
called land-locked salmon, but the life history of the 
