We gather from our most recent correspondence with Mr Shaw, (Letter of 8th June 1843,) that he does not regard the range in the spawning period to be followed by a corresponding range in the departure of smolts towards the sea, and in their return from it as grilse. He has found a considerable diversity of time in the assumption of the silvery coating even among individuals of the very same family. "I do not," he observes, "recollect an instance where there were not individuals of each brood reared in my ponds, which assumed the migratory coating several weeks before the brood in general had done so; and these individuals would have migrated accordingly, and reappeared as grilse all the sooner." As the hatching and growth of salmon smolts and other fish, is regulated in a great measure by the temperature of the water in which they dwell, it is very probable that ova deposited late in the season, (say the month of March,) may, in consequence of the great increase of temperature, be hatched much more rapidly than those spawned in mid-winter, and so, by the end of a couple of years, no great difference will exist between them. We remember that, in one of Mr Shaw's earlier experiments, it is stated that he took occasion to convey a few ova in a tumbler within doors, where the temperature ranged from 45° to 47°. They were hatched in thirty-six hours, while such as were left in the stream of the pond, in a temperature of 41°, did not hatch until the termination of seven subsequent days. The whole had been previously one hundred and six days in the water, under a considerably lower temperature.