METHODS OF INVESTIGATION. 29 



we find that the last three groups agree most closely. With one solitary 

 exception the differences are, as a rule, very small, and hardly ever exceed 

 a small percentage of the average length of each year-class. Between the 

 average of the whole of the material examined and the corresponding 

 averages for the eleven fish selected at random, it is only in one instance, 

 viz., the seventh class, that we find a difference of about 16 per cent. This 

 exception may, however, be due to the fact that the figures for the last four 

 winters of the eleven fish group are based on one single individual, and 

 cannot, therefore, be taken as an average representation. 



The results obtained from these investigations seem to me to prove 

 sufficiently that we can obtain fairly reliable illustrations of the rate of 

 growth from calculations based on a comparatively small amount of 

 material. It is hardly necessary to add that the specimens should be 

 selected with judgment, and also with some knowledge of local conditions 

 and of the maximum size of fish frequenting the waters under investiga- 

 tion. The results should also not be pressed too far or without allowance 

 for possible sources of error. Still, it is important to know that for all 

 practical purposes it has been found possible to form a fair idea of tne rate 

 of growth of fish in any particular locality by merely examining a 

 comparatively small number of individuals. 



