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 May 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 Limneus peregra had taken up their abode among the 
aquatic plants. 
NEGATION. 
I. Not true Salmon?—I had Dr. Giinther’s permission to state 
that in his opinion the specimens reared in the Gardens (cf. P. Z. 8. 
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 ver- 
tebree, of the cacal appendages, and of the scales; the other six 
characters which Dr. Giinther considers trustworthy in the classifi- 
cation of the Salmonide are not so applicable in the present instance. 
A tabular view, moreover, may be more readily appreciated ; hence 
I place in series the formulze appertaining to true Salmon, our two 
specimens, and such forms as are the most likely to have been intro- 
duced into the Gardens and mistaken for Salmon. The formule are 
* See ‘ The Field,’ June 13, 1868. 
+ Through Mr. Tegetmeier’s interest, the proprietors of ‘The Field’ have 
kindly permitted me the use of their woodcuts illustrating the phenomenon here 
cited (see p. 35). 
