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Show 1870.] IN THE GROWTH OF SALMON. 31 remainder of the ova left in charge of the correspondent to receive widely different treatment-hatching to be carried on in the open air, and the tiny fish, once out, confined in a pond. Reared to the Smolt condition, when the migratory restlessness occurred, some might be marked and allowed to go seaward, the condition of those left behind being noted. During the second or third season, as the case might be, others to be allowed to depart, whilst a few are permanently retained in the pond. Three years or less from the commencement of the experiment, in the event of a marked grown Grilse or Salmon being caught, specimens from the Society's tanks, the open-air pond, and it to be rigidly compared side by side. In the intervals specimens of the progressive ages and stages to be preserved in spirits, and, as apparent changes take place, figures and annotations thereon duly registered. The result of experiments conducted somewhat in the above fashion would, I consider, conclusively prove whether or not Salmon are temporarily or definitely arrested in their development when retained for a considerable period in fresh water. At all events all chance of the denial of the parentage of the fish would be obviated. Or, again, if the breeders of Salmon, say at the stock-ponds in Perthshire, could be induced to fertilize the ova of a full-grown Salmon, and transmit the same to the Society, I venture to say the ova would be attentively watched during the process of hatching, and afterwards the phenomena and stages of growth duly recorded. Furthermore, could the bodies of the parents, male and female, be likewise transmitted to London for identification, all possibility of error would be prevented. As appears plain from what has happened with those already reared in the Zoological Gardens, it is of the utmost importance that the parents should bear witness of the ova being those of genuine Salmo salar. It is, indeed, much to be desired that some such well-attested observations should be pursued; for notwithstanding the asseverations of several trustworthy observers, subsequently to be cited, there still remains a lurking suspicion that error of data may have crept in. I urge therefore upon pisciculturalists, and such as are interested in solving a physiological, or, rather, zoological problem of high value, the benefit science would derive from the authentication or denial of the alleged circumstantial evidence. This is m y plea for intruding the above suggestions and further memoranda upon the Society. I trust that this second notice may stir up those at home, or fish-rearers abroad, to follow out the investigation. I may premise that I have not entered on the task in a controversial mood, but to incite further research on the matter. Moreover it is possible those interested in the question may wish to refer to the data, be they merely asserted or be they proven, concerning the rearing and detention in pure fresh water for so long a period of fish considered to be Salmon. It may be pardonable on m y part, then, to examine more narrowly than heretofore the grounds of opinion, favourable or adverse, especially as the whole matter is one involving biological laws of the |