180 BRITISH FRESH-WATER FISHES 
own opinions in competition with his. I have bestowed 
a great deal of attention upon the habits of Sa/lmonide ; but 
I am neither anatomist nor physiologist. Upon the question, 
therefore, of what degree and constancy of variation in 
structure should be recognised as constituting a distinct 
species, my opinion would be worthless. But, having observed 
how completely the offspring of some of Dr. Giinther’s species, 
such as the Loch Leven trout (Salmo levenensis), lose their 
hereditary characteristics in adapting themselves to novel 
environment ; how quickly the ordinary brook trout (Sa/mo 
fario) acquires the appearance of the Loch Leven race when 
submitted to similar conditions of food and habitat ; lastly, 
how imperceptible are the gradations between the different 
so-called species—I incline to the opinion of Fatio, Day, 
and other ichthyologists, which accounts for the so-called 
specific differences between the various kinds of sea, lake, 
and river trout as the transient effects of food, climate, 
and local environment. 
In effect, I have taken a cowardly middle course, which will 
meet with the approval of neither party, by adopting Dr. 
Giinther’s subdivision of the genus Sa/mo into two groups— 
Salmones and Salvelini, salmon and char—and designating as 
species the leading types of each. I feel reassured in doing so 
by the fact that Dr. Gutnther’s classification is admittedly 
tentative, was formulated nearly forty years ago, and that some 
of his minor specific differences can scarcely be said to have 
stood the test of subsequent observation. 
In one respect all the genus Sa/mo, as well as some species 
of other genera of Salmonide, possess in common a remarkable 
and highly suggestive characteristic. Greatly as the adults of one 
species may differ in appearance from those of another, yet 
hardly more so than individuals of the same species differ among 
themselves, they all pass through a stage when not only all 
members of the same species are alike, but it is scarcely possible 
to distinguish one species from another. Yearly salmon and 
