A STUDY ON TROUT AND YOUNG SALMON. 



257 



to express it that way, its relation to the length of the tail, 

 3) the more or less prominent slenderness of the tail. 



The size of the scales may be determined as other investiga- 

 tors have done, by counting their number in a row over a cer- 

 tain measured portion of the body and referring this length to 

 the length of the fish. However as I find this method too imprac- 

 ticable, I have deemed it better to count the number between 

 two definite points on the body e. g. in the oblique row of scales 

 running from the hindpart of the base of the adipose fin down 

 to the lateral fine. I have included the perforated scale of 

 the lateral fine. 



The relation of the anal fin to the length of the tail may 

 be brought out by dividing the latter by the length of the anal 

 fin. The result will be a coefficient which I call "Tail coefficient I." 



The more or less pronounced slenderness of the tail may 

 also be expressed as a relationship between the length and mini- 

 mum altitude or depth of the tail — "Tail-coefficient II." In the 

 subjoined illustration (fig. 1) these different lines of measurement 

 are indicated and explained. 



The method employed in examining the spechnens is illu- 

 strated by the following example. 



Total length of . 

 the fish. ^ 



B 



G 



D 



25 cm. 



15 



2,5 cm. 



2 cm. 



1,5 cm. 



Tail coefficient I = 



= §-2-5 = 0'8"- 



» » 



11 = 



G 

 ~ D 



1,5 ^' 



33. 



In this way large numbers of salmon and trout have been 

 measured. Of course they have all been immature fish. To 

 see if the relationship of these different characteristics altered 



Nyt Mag. f. Naturv. XXXXII. III. 17 



