254 KNUT DAHL. 



the reduction of the innumerable „Species" of salmonids, flooding 

 the systematical literature of former days, deserves every 

 aknowledgement. 



As I have shown, the lack of material of the „forell" stage 

 of the real salmon has prevented a perfect distinction between 

 salmo solar and salmo trutta, a gap wich according to my 

 experience has been very difficult to fill. 



This deficenecy and supplementing it with specimens be- 

 longing to the relict salmon form of middle Sweden in my 

 opinion suffices to explain, how professor Smitt, undoubtedly 

 the scientist, who on this subject has excercised the greatest 

 care and drawn the utmost consequences from his researches, 

 has not been able to separate the two species. 



In the following pages I will describe the youger stages of 

 the salmon compared with trout of corresponding sizes. I will 

 commence with the stages in wich the fishes leave the rivers and 

 further describe them during their developement. The larger 

 stages from ca. 45 cm. and upwards are not worth describing, 

 as they easily my be dish'nguished by people not wholly 

 ignorant on the subject. 



Certainly previous investigators have given quite accurate 

 descriptions of fry and emigrants belonging to thise species; 

 but for sake of completeness and in order that this work my be 

 useful to those who might wish to use it for the specific deter- 

 mination of such fishes, I also incclude the fry. 



To begin with however I wish from a general point of 

 wiew to discuss some principles, wich according to my opinion 

 are fundamental to the specific description. 



Describing a species, the scientist is hardly able to do more 

 than as accurately as possible to detail the image wich the 

 peculiarities of the species in question, presents to his senses, 

 and by means of wich he may recognise the species in single 

 individuals. 



