The powan, another of the mysterious fish of Scotland, is also considered to be a fresh-water herring, and thought to be confined exclusively to Lochlomond, where they are taken in great quantities. It is supposed by persons versed in the subject that it is possible to acclimatise sea fish in fresh water, and that the vendace and powan, changed by the circumstances in which they have been placed, are, or were, undoubtedly herrings. The fish in Lochlomond also gather into shoals, and on looking at a few of them one is irresistibly forced to the conclusion, that in size and shape they are remarkably like the common herring. The powan of Lochlomond and the pollan of Lough Neagh are not the same fish, but both belong to the Coregoni: the powan is long and slender, while the pollan is an altogether stouter fish, although well shaped and beautifully proportioned. I could analyse the natural history of many other fish, but the result in all cases is nearly the same, and ends in a repeated expression that what we require as regards all fish is the date of their period of reproduction; all other information without this great fact is comparatively unimportant. It is difficult, however, to obtain any reliable information on the natural history of fish either by way of inquiry or by means of experiments. Naturalists cannot live in the water, and those who live on it, and have opportunities for observation, have not the necessary ability to record, or at any rate to generalise what they see. No two fishermen, for instance, will agree on any one point regarding the animals of the deep. I have examined every intelligent fisherman I have met within the last ten years, numbering above one hundred, and few of them have any real knowledge regarding the habits of the fish which it is their business to capture. As an instance of fishermen’s knowledge, one of that body recently repeated to me the old story of the migration of the herring, holding that the herring comes from Iceland to spawn, and that the sprat goes to the same icy region in order that it may fulfil the same instinct.