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Show 36 DR. J. MURIE ON IRREGULARITY [Jan. 13, and the extent of the water in which they abide. Many facts might be adduced in support of this ; but one of recent occurrence may serve the purpose of illustration*. The experiments at Stormont-field, in Perthshire, already adverted to, are too well known to need further comment; suffice it to say that there can be little doubt of these ponds containing the produce of genuine Salmo salar. On the 20th of M a y 1868, at the above piscicultural establishment, " Peter of the Pools" (the nom de plume of an experienced Salmon-rearer) observed great variation in the size of the smolts of the same age-some of the two year-old fish being fully a fourth larger than others, and their bodies proportionally plump. This increased growth was found to be dependent on their feeding on molluscous animals; for in the pond which the large Smolts inhabited vast quantities of Limnceus peregra had taken up their abode among the aquatic plantsf- NEGATION. I. Not true Salmoni-I had Dr. Giinther's permission to state that in his opinion the specimens reared in the Gardens (cf. P. Z. S. 1868, p. 247) are not true Salmo salar, as he considers their history a doubtful one, and furthermore, in some respects, they disagree with the characters assigned by him to that species. He justly lays stress upon the weak point that the ova may or may not have been the produce of a female Salmo salar, and may or may not have been impregnated by the milt of a male of the same species. He thinks that among the immense numbers of Salmon-ova yearly sent off from the hatching-establishment at Huningue on the Rhine, there is likelihood of mixture occasionally occurring in the transit, and also that fish which are not true Salmon may be mistaken for them and thus error arise. The chance that fortuitous circumstances might give rise to the last-mentioned error has already to some extent been admitted. It is well to remember, however, that Salmon-ova are distinguishable from those of the Great-Lake Trout, with which they may have been most readily confounded, by their greater size and deeper yellowish tint. Now as regards constant characters defining the species, and thereby, by the absence of such, excluding the imperfectly developed specimens from being considered as representatives of Salmo salar, Linn., I shall take three into consideration-the number of the vertebrae, of the caecal appendages, and of the scales; the other six characters which Dr. Gunther considers trustworthy in the classification of the Salmonidae are not so applicable in the present instance. A tabular view, moreover, may be more readily appreciated; hence I place in series the formulae appertaining to true Salmon, our two specimens, and such forms as are the most likely to have been introduced into the Gardens and mistaken for Salmon. The formulae are * See ' The Field,' June 13, 1868. t Through Mr. Tegetmeier's interest, the proprietors of ' The Field' have kindly permitted m e the use of their woodcuts illustrating the phenomenon here cited (see p. 35). |