274 How to obtain it. 
now finding out many things about the genus Sa/mo that were 
unknown and unthought of a few short years ago. 
It is well known that trout in their natural haunts assume 
endless varieties; indeed it would be difficult in most cases to 
find two exactly alike. We find in a great many instances races 
of yellow, silvery and dark-coloured trout (often called black trout) 
inhabiting the same lake. In some streams which are frequented 
by marine or anadromous forms we often find a considerable 
variety, and every connecting link may be obtained at times 
between sea-going and fresh-water forms, as for instance, Salmo 
trutta and Salmo fario. In certain cases undoubtedly these fish 
have crossed with each other, and it may be their descendants 
have crossed again, thus producing considerable variations, 
quite enough to puzzle the older naturalists who were not fish 
culturists, and therefore had not the same facilities for ascertaining 
the real truth. When we come to deal with these fish in a practical 
manner, within the inclosed boundaries of a fish farm, we find out 
that there is in reality very little, if any, difference between the 
races, beyond the inherited greater migratory instinct of the sea- 
going kinds. They spawn here at the same time and in the same 
places, and I have more than once found ¢vu¢¢a paired with fario. 
The mingling of the two races in our streams is inevitable, and 
knowing what we do now as to the fertility of the offspring there 
can be no doubt whatever that the two forms do at times get 
considerably mixed, 
Occasionally, owing perhaps to some exceptional circum- 
stance, such as rain after dry weather, or it may be a sudden 
change of temperature, the streams frequented by the spawning 
fish become crowded, and the involuntary mingling of the two 
races must, one would think, occasionally take place. I have 
seen both forms spawning in such close proximity that I am fully 
convinced that milt and ova of the two races must occasionally 
come in contact, and impregnation take place. Anyhow, we have 
the intermediate varieties occurring in Nature and we can bring 
about exactly the same results by artificial means, 
We know that in the human family some individuals have a 
much greater propensity for roaming than others, and some races 
of men exist who make periodical migrations. Why should not 
