382 Proceedings of the British Association, 



In proportion as the genus Salmo is now circumscribed within it» 

 natural limits, so much the more is it difficult to characterise the 

 various species ; and I have no fear of being contradicted when I 

 affirm, that since no one has devoted himself to their history, so no 

 one has yet succeeded in determining, with any degree of precision, 

 their distinctive characters. The greatest obstacle to the solution 

 of this problem arises from our ignorance of the accuracy of the 

 characters hitherto employed to distinguish the several species, the 

 one from the other. We have especially attached ourselves to the 

 form of the head, and to the arrangement of the colours ; but these 

 two particulars are much too variable to supply precise charac- 

 ters. As to the variation in the colour, we may^^say it is infinite. 

 There are, however, two circumstances which especially modify 

 the tints of the salmon tribes, namely, their age, and the season of 

 the year. The younger fish are, in general, much more spotted 

 than the older ones, whose tints become more and more uniform. 

 The Salmo Hucho, for example, with violet spots more or less dis- 

 tinct, has, when young, large black transverse bands upon the back, 

 down to the middle of its sides. In the second and third years of 

 its existence, these band* break up into black spots, less deep in co- 

 lour, and they disappear more and more, till in its latter years the 

 fish acquires a colour which is almost uniform. The Salmo lacus- 

 tris of Linnaeus, when young, has large black and ocellated spots 

 upon all the superior parts of its body ; but from the third year 

 they diminish, and ere long they entirely disappear. The Salmo 

 Umhla^ so long as it is young, is of a uniform greenish-yellow co- 

 lour, with the abdomen white, and at a later period of life these 

 tints assume a deeper hue — of a more lively green, and finally pass 

 into a blackish-green. The abdomen soon becomes silvery-white, 

 afterwards yellow and orange coloured, and then of a golden lus- 

 tre. Its flanks are very soon adorned with ocellated yellow spots 

 more or less distinct, but ere long there are no spots at all. In 

 the Salmo Farioy the spots vary even more. In the young they 

 are found yellow, green, brown, even black and violet, also blacl^ 

 and red, but in the long run they all entirely disappear. I have 

 also noticed that the seasons have an influence on the colours of 

 the difl^erent kinds of Salmo. It is during the autumn, and at the 

 time of the greatest cold, that is to say in October, November, De- 

 cember, and January, that their tints are most brilliant, and the 

 colours become more vivid by the accumulation of a great quantity 

 %£ coloured pigment*. We might almost say that these fishes be- 



