permanent inhabitants of a loch in the island of Lismore, Argyllshire.  Similar facts have been recorded by other naturalists, though, upon the whole, in a somewhat vague and inconclusive manner.  We have it in our power to mention a very marked example.  When certain springs were conducted, about twenty years ago, from the slopes of the Pentland Hills, near Edinburgh, into that city, which Dr Johnson regarded as by no means abundantly supplied with the “pure element of water,” it was necessary to compensate the mill-owners by another supply.  Accordingly a valley, (the supposed scene of Allan Ramsay’s “Gentle Shepherd,”) through which there flowed a small stream, had a great embankment thrown across it.  After this operation, of course the waters of the upper portion of the stream speedily rose to a level with the sluices, thus forming a small lake, commonly called the “Compensation Pond.”  The flow of water now escapes by throwing itself over the outer side of the embankment, which is lofty and precipitous, in the form of a cataract, up which no fish can possibly ascend.  Yet in the pond itself we have recently ascertained the existence of sea-trout in a healthy state, although such as we have examined, being young, were of small size.  These attributes, however, were all the more important as proving the breeding condition of the parents in a state of prolonged captivity.  It is obvious that sea-trout must have made their way (in fulfilment of their natural migratory instinct) into the higher portions of the stream prior to the completion of the obstructing dam; and as none could have ascended since, it follows that the individuals in question (themselves and their descendants) must have lived and bred in fresh water, without access to the sea, for a continuous period of nearly twenty years.  This is not only a curious fact in the natural history of the species, but it is one of some importance in an economical point of view.  Sea-trout, as an article of diet, are much more valuable than river-trout; and if it can be ascertained that they breed freely, and live healthily, without the necessity of access to the sea, it would then become the duty, as it would doubtless be the desire, of those engaged in the construction of artificial ponds, to stock those receptacles rather with the former than the latter.[25]

[24] Mr Shaw informs us, moreover, that if those individuals which have assumed the silvery lustre be forcibly detained for a month or two in fresh water, they will resume the coloured coating which they formerly bore.  The captive females, he adds, manifested symptoms of being in a breeding state by the beginning of the autumn of their third year.  They were, in truth, at this time as old as herlings, though not of corresponding size, owing to the entire absence of marine agency.

[25] Another interesting result may be noticed in connexion with this Compensation Pond.  The original streamlet, like most others,