It is certainly, however, difficult to explain the motives by which the early spring salmon are actuated in ascending rivers, seeing that they never spawn till autumn at the soonest. We must remember, at the same time, that they are fresh-water fishes, born and bred in our own translucent streams, and that they have an undoubted right to endeavour to return there when it suits their own inclination. It may be, that although the ocean forms their favourite feeding-ground, and their increase of size and continuance in high condition depend upon certain marine attributes, which, of course, they can find only in the sea, yet the healthy development of the spawn requires a long-continued residence in _running_ waters. We have ascertained, by experiment, that the ova of salmon, after being deposited, will make no progress in still water; and we cannot illustrate this portion of the subject better than by transcribing a paragraph from a letter, addressed to us in spring, (11th April 1843,) by Mr Andrew Young of Invershin, the manager of the Duke of Sutherland's extensive salmon fisheries in the north of Scotland:--"You are aware that it has been asserted by some of our wisest doctors, that salmon spawn in the sea and in lochs, as well as in rivers. However, as doctors are proverbially allowed to differ, I have this winter been trying to test the fact in the following manner: At the same time that I deposited the spawn from which I made my other experiments, I also placed a basket of the same spawn, with equal care, in a pool of pure still water from the river Shin; and I soon found that, while that which was placed in the running pools was regularly progressing, every particle put into the still water was as visibly degenerating, so that, by the time the spawn in the running pools was alive, that in the still water was a rotten mass. I must therefore say, from the above experiment, that rivers and running streams are the places fixed by nature for salmon to hatch their young." "I would also," says our correspondent in a subsequent portion of his letter, "mention an additional experiment on another point. It has been very generally asserted that intense frost injured the spawn of salmon; and in this opinion I was myself, in some measure, a believer. But as nothing but truth will stand a proper test, I turned my attention to this subject also. During the time of our severest frost, I took a basket of spawn, and placed it in a stream, where for three days it continued a frozen mass among the ice. I then placed the basket again in the running pond from whence it had been taken, and carefully watched the effect. I found that, although exposure to extreme cold had somewhat retarded the progressive growth, it had not in the slightest degree destroyed vitality. I am therefore satisfied, that unless frost goes the length of drying up the spawning beds altogether, it does not harm the spawn, further than by retarding its growth during the actual continuance of