was naturally stocked with small “burn-trout,” which never exceeded a few ounces in weight, as their ultimate term of growth.  But, in consequence of the formation above referred to, and the great increase of their productive feeding-ground, and tranquil places for repose and play, these tiny creatures have, in some instances, attained to an enormous size.  We lately examined one which weighed six pounds.  It was not a sea-trout, but a common fresh-water one—­Salmo fario.  This strongly exemplifies the conformable nature of fishes; that is, their power of adaptation to a change of external circumstances.  It is as if a small Shetland pony, by being turned into a clover field, could be expanded into the gigantic dimensions of a brewer’s horse.

Having narrated the result of Mr Shaw’s experiment up to the migratory state of his brood, we shall now refer to the further progress of the species.  This, of course, we can only do by turning our attention to the corresponding condition of the fry in their natural places in the river.  So far back as the 9th of May 1836, our observer noticed salmon fry descending seawards, and he took occasion to capture a considerable number by admitting them into the salmon cruive.  On examination, he found about one-fifth of each shoal to be what he considered sea-trout.  Wisely regarding this as a favourable opportunity of ascertaining to what extent they would afterwards “suffer a sea change,” he marked all the smolts of that species (about ninety in number) by cutting off the whole of the adipose fin, and three-quarters of the dorsal.  At a distance, by the course of the river, of twenty-five miles from the sea, he was not sanguine of recapturing many of these individuals, and in this expectation he was not agreeably surprised by any better success than he expected.  However, on the 16th of July, exactly eighty days afterwards, he recaptured as a herling (the next progressive stage) an individual bearing the marks he had inflicted on the young sea-trout in the previous May.  It measured twelve inches in length, and weighed ten ounces.  As the average weight of the migrating fry is about three and a half ounces, it had thus gained an increase of six and a half ounces in about eighty days’ residence in salt water, supposing it to have descended to the sea immediately after its markings were imposed.  In this condition of herlings or phinocks, young sea-trout enter many of our rivers in great abundance in the months of July and August.

On the 1st of August 1837—­fifteen months after being marked as fry, on its way to the sea—­another individual was caught, and recognised by the absence of one fin, and the curtailment of another.  This specimen, as well as others, had no doubt returned, and escaped detection as a herling, in 1836; but it was born for greater things, and when captured, as above stated, weighed two pounds and a half.  “He may be supposed,” says Mr Shaw, “to represent