A STUDY ON TROUT AND YOUNG SALMON. 269 



characters mainly belonging to salmon of more advanced develop- 

 ment. 



This phenomenon is explained by the above-mentioned facts. 

 I only mention it here to prevent the presumption that the sal- 

 mon, once emigrated, must needs present the following characters. 



This will specially relate to the sizes between 10 and 

 20 cms. 



As an illustration of the appearance of salmon and trout, 

 after the juvenile characters have been discarded, the drawings 

 on PI. II and III may serve. Salmon and trout are here re- 

 presented, in pairs for closer comparison. 



The upper figure in PI. II is a trout 21 cms. long, the lower 

 one a salmon 21,5 cms. long. The trout was caught in a seine 

 in the Trondhjem fiord; the salmon is one of two, I found in 

 the Bergen museum, reared by Mr. Grude in a freshwater-pond 

 at Jæderen. 



The upper figure on Pi. Ill is a trout 25,5 cms. long, 

 caught in the Trondhjem fiord, and the lower one a salmon 28 

 cms. long reared in my aquarium at the Trondhjem Biol. Station. 



The drawings in these as well as in PI. I are executed by 

 Mr. A. Dircks taxidermist to the Academy of Sciences in Trond- 

 hjem. All relations are carefully measured by compasses, redu- 

 ced and entered on the drawings; they have been also twice 

 tested and corrected in the same manner by me. 



The caudal fin in the salmon drawn on PI. II was worn, 

 somewhat, during life in the aquarium and the flukes were 

 smaller than represented in the figure. The points of the 

 flukes are constructed with the aid of one of the specimens 

 (28 cms. long) I found at the University of Christiania and 

 which had been kept so long in spirits as to render it in other 

 respects less fit as material, for a representative drawing. 



The principal characteristics of distinction between sal- 

 mon and trout at this stage will be found under the following 

 features. 



