10 THE AGE AND GROWTH OF SALMON AND TROUT. 



NUMBER AND PERCENTAGE OF SCALES ON WHICH THE LAST WINTER-BAND 



WAS SITUATED. 



Here we find that the last winter-band lies close to the edge of the scale 

 throughout January, February, and March, and it is not until April that a 

 few fish begin to show the commencement of summer growth at the edge 

 of the scales. In May, June, and July the summer-zone becomes larger 

 and larger, in exactly the same manner as we found to be the case with 

 Norwegian fish. 



In my opinion these investigations have made it pretty clear that the 

 narrow, close-lying, branching rings are in fact winter-zones, whereas the 

 summer- zones are formed of broad, boldly-marked and less branching rings 

 which lie further apart. At any rate, the formation of these two different 

 series of growth-rings or zones takes place in the winter or summer half 

 of the year respectively. 



If one examines Figs. 9 to 11 (Plates II., III., IV.) it will be evident that 

 one can easily and unmistakably distinguish the different annual rings 

 at a glance. This is, however, not always the case, and a certain amount 

 of practice is required if this method of examination is to be employed 

 for statistical purposes. In addition, it is necessary that any analysis 

 made should be based on as large an amount of material as possible, 

 so that in doubtful cases one can obtain assistance from the bulk of the 

 specimens examined, and also render the few errors of analysis which may 

 arise of little importance by the overwhelming weight of the quantity 

 examined. 



One of the chief difficulties and especially to beginners, is the fact that 

 scales may sometimes become slightly displaced in the process of growth, 

 and consequently present a distorted picture of the subsequent growth in 

 relation to what has previously taken place. In the next place there may 

 occur with some individuals secondary checks in the ring formation during 

 summer growth, and which are indicated by two or three rings or more 



