4 ESDAILE, Scales of three Specimens of Salmo salar. 



The annuli are very irregular. They branch frequently, 

 giving off both long and short branches, and they are at 

 very varying distances from one another. The summer 

 and winter growths are not always clearly defined. The 

 decrease in the rate of growth at the beginning of the 

 winter is often very gradual, and therefore the annuli 

 gradually become closer together, so that it is difficult to 

 say where the summer growth ceases and the winter 

 growth commences. Dr. Turnbull, writing in The Field, 

 gives an account of his method of counting the annuli; 

 he distinguishes between what he calls "main" and 

 "duplicate" annuli, stating that the "main annuli may 

 split or fork in the neighbourhood of the long axis to form 

 duplicate annuli." This distinction, however, seems to be 

 most unsatisfactory. The annuli are all so different. No 

 two branches are alike, and there might be a score or 

 more of cases on one scale only where a heated discussion 

 might be held as to whether the annuli in question are to 

 be called "main" or "duplicate." After distinguishing 

 between these two kinds of annuli. Dr. Turnbull counts 

 only the " main " annuli, and uses only these for the 

 comparison of the scales from different fish. Mr. Johnston 

 does the same thing, counting what he calls the "main 

 stems " and not the " off-shoots." All investigators of the 

 scales of fish state that as the fish grows, the size of the 

 scale is increased, and annuli are formed at intervals. 

 Each annulus then must show that growth has taken place, 

 and growth must have taken place in a particular part 

 where a so-called" duplicate "annulus is formed; and yet, 

 according to some, this special kind of mark of growth is 

 to be ignored. Surely this method renders the work 

 almost useless when endeavours are being made to 

 ascertain the age and rate of increase of the fish as 

 indicated by the scales. 



