I frequently afterwards witnessed the same thing, and always found the same difference of sexes; in fact, there was generally no difficulty in distinguishing the male from the female, without taking them out of the water: the latter might be readily known by the enlargement of her body, and the former by a still more incontestable token. I have been induced to describe this more minutely than I otherwise should have done, in consequence of the mystery in which the propagation of fish has been wrapped hitherto; and I am not aware that what I have described has been witnessed by anyone before--at least I don't know that it has been recorded. I caught half-a-dozen Lampreys, four males and two females, and preserved them in spirits, and these I now forward to you. I am unable to give the same information concerning the large Lamprey, having never seen it in the act of spawning; but I have repeatedly caught both milters and spawners of species with the milt and roe as distinctly visible in them as it is in the Salmon or any other fish. I am of opinion that the _P. marinus_ and the _P. fluviatilis_ are distinct species, for the following reasons:--1st. Because the latter stays with us the whole year, while the former only ascends the rivers to spawn, and then returns to the sea immediately. 2nd. Because fish that are in the habit of descending to the sea, never (unless the small Lamprey be an exception to the general rule) arrive at maturity [13] until they have visited it; and, 3rdly, because there are no intermediate sizes (at least in the Ribble) between the one which, although only six or seven inches long, and an ounce in weight, is yet capable of propagation, and the one of a pound. Not having one of the larger kind to refer to, I am unable to point out any specific difference of form. (May 2nd, 1832.) * * * * * ON THE SPAWNING OF THE MINNOW.