1884.] HYBRIDS AMONG THE SALMONID^. 23 



On exatniiiing an American Charr, Sulmo fontinalis, in the parr- 

 stage, and 2>l inches in length, the scales covering the body on their 

 outer surface'were found to be covered and bound down to one another 

 by a covering of epidermis (which in its turn was much concealed by 

 a thick layer of mucus); the same appearance was present in a Sal mo 

 levenensis 4 inches in length, while in a 8almon-parr, 6 inches long, 

 a change had commenced in some regions of the body. The hind 

 portion of the exposed part of each scale, sometimes to as much as 

 one third or even one half, being silvery, or rather transparent, per- 

 mitting the silvery lustre to shine through, but not so the basal 

 portion, which retained more of the parr-colour. On placing a 

 needle under these scales, the transparent or silvery part could be 

 readily elevated ; it was no longer bound down by epidermis, as in 

 younger fish, while but very little mucus was present. Among the 

 silvery smolts this apparent denudation of the scales had been 

 carried to a greater extent, the epidermis being seemingly merely 

 present across its base (except where black or orange spots existed), 

 and as a consequence a silvery scale with more or less dark edges 

 was .seen. Should the scale of a smolt be raised, it appears as if 

 on the sides and n)ost of the body of the fish it were merely attached 

 at its base and placed in a pocket of the epidermis, and nowhere in 

 the body is any new layer of scales developed, or an increased thick- 

 ness put on, but, on the contrary, the epidermal covering seems to 

 become removed in the smolt-stage, thus occasioning their trans- 

 parent and consequent silvery appearance, which is continued through 

 life. Owing to the epidermis being less removed from the scales of 

 the back, and being present over the scaleless head, these portions 

 retain a darker colour. 



A hybrid between S. salar and >S'. levenensis, at 7-4 inches in 

 length, shows a portion of tlie outer edge of each scale already 

 denuded of epidermis ; and although I do not propose in this paper 

 to enter upon the question of colour, I may remark that the lateral 

 bands or finger-marks come into more prominent view when the 

 scales and attached epidermis are removed, rendering it probable 

 that they are found in the cutis. The black spots, or at least some 

 of those which are seen on the body, are in the epidermis, and can be 

 removed with that structure ; while on removing a scale, the epi- 

 dermal pocket in which its base lies is found of a dark and often 

 black colour. If the epidermis of a young fish is placed under the 

 microscope, it is more or less filled with fine black dots ; consequently 

 the absorption of this structure, irrespective of its leaving the silvery 

 portion uncovered, removes what must add a darker tinge to the 

 fish. In like manner a portion of the red or orange dots may be 

 external to the scales, as in the epidermis or in the structures below 



aud Ganoids. The scales increase in size by apposition, their basal portion 

 forming the matrix being pai-t of the cutis, in a similar way to finger-nails 

 growing out of the nail-fold. There are two main classes of these scales, one 

 retaining an embryonic condition, as in some parts of a Mackerel, &e., while 

 tbose of the Salmon, which attain a larger size, break tLrough the epidermal 

 layer, and thus become partially Iree." 



