256 KNUT DAHL. 



In two species, so closely allied as trout and salmon, one 

 must however obviously expect the different relations of the body 

 to vary, especially so, when at least one of the species is known 

 to be disposed to variation. 



When man, apes, birds etc. show individual variation 

 vithen the limits of the species, we must also in the present 

 case be prepared to meet it, and in the examination of large 

 numbers of individuals the variation vill sone be observed. 



Every form, every relation in an organism may be metri- 

 cally described and expressed by figures. A series of investi- 

 gators have largely employed and still employ the metrical 

 method. In this however I think they very often are wrong. 

 The main object of a diagnostic description is to be practical, 

 and now there is nothing, wich in a more unpractical way 

 denotes the form, at least in fishes, than the figure. As professor 

 Hervig once said, there is nothing to prevent us from correctly 

 describing the face of a man metrically, but undoubtedly we 

 should find it difficult and unpractical to recognise our friends 

 by means of such a table of figures or formula. 



I openly confess that great difficulties are in the way of 

 finding aedquate expressions for a difference in specific form 

 wich mainly is brought to our brain through the eye; but an 

 adequate carefull repræsentation in words aided by exact draw- 

 ings is undoubtedly in most cases preferable to figures. 



When I in the fallowing have availed myself of measure- 

 ments, it is not with the intention of preparing a table of figures 

 by means of wich salmon and trout may be distinguished. 



I only wish to produce a graphic, through the eye easily 

 perceptible, representation of the progress of a few of the abor- 

 mentioned characters in salmon and trout, the individual varia- 

 tion considered. 



Among the peculiarities and different relations wich destin- 

 guish salmon and trout may be mentioned 1) the different size 

 of the scales, 2) the different size of the anal fin or if we like 



