the most powerful reasons for _resisting_ or _removing_ obstructions in the estuary of a river.” The riddle of this double migration of the salmon is likely still to puzzle us. It is said that the impelling force of the migratory instinct is, that the fish is preyed upon in the salt water by a species of crustaceous insect, which forces it to seek the fresh waters of its native river; again, that while the fresh water destroys these sea-lice a new kind infests it in the river, thus necessitating a return to the sea. My own experience leads me to believe that salmon can exist perfectly well in the fresh water for months at a time, suffering but little deterioration in weight, but never, so far as I could ascertain, growing while in the fresh streams, although it is certain they feed. It is a well-known fact that the parr cannot live in salt water. I have both tried the experiment myself and seen it tried by others; the parr invariably die when placed in contact with the sea-water. Mr. William Brown, in his painstaking account of _The Natural History of the Salmon_, also bears his testimony on this part of the salmon question:—“Until the parr takes on the smolt scales, it shows no inclination to leave the fresh water. It cannot live in salt water. This fact was put to the test at the ponds, by placing some parrs in salt water—the water being brought fresh from the sea at Carnoustie; and immediately on being immersed in it the fish appeared distressed, the fins standing stiff out, the parr-marks becoming a brilliant ultramarine colour, and the belly and sides of a bright orange. The water was often renewed, but they all died, the last that died living nearly five hours. After being an hour in the salt water, they appeared very weak and unable to rise from the bottom of the vessel which contained them, the body of the fish swelling to a considerable extent. This change of colour in the fish could not be attributed to the colour of the vessel which held them, for on being taken out they still retained the same brilliant colours.” All controversies relating to the growth of salmon may now be held as settled. It has been proved that the parr is the young of the salmon; the various changes which it undergoes during its growth have been ascertained, and the increase of bulk and weight which accrues in a given period is now well understood. But we still require much information as to the “habits” of fish of the salmon kind.