24 THE AGE AND GROWTH OF SALMON AND TROUT. 



the scale-covered portion of the body. This difference, however, is not large, 

 at any rate in the case of fresh-water trout.* 



There is also some uncertainty in connection with the exact demarca- 

 tion of the winter-band, as this is not an exact line, but consists of a 

 collection of very narrow growth-rings lying close to one another, whose 

 position it is necessary to define. 



It is therefore evident that this method may suffer from several small 

 errors, but after some practice and with careful investigation these errors 

 will tend to disappear. 



My main object, however, has been to endeavour to prove by practical 

 means whether calculations based on this method of examination will enable 

 us to draw up a growth-curve as reliable as one obtained by ordinary methods 

 of analysis of age and size, and whether we can accordingly arrive at 

 sound conclusions as to the rapidity of growth by the examination of 

 comparatively few individual specimens. 



In order to make this point clearer I will give the results of a few 

 analyses which I have made. 



Out of a number of examples of salmon from Lister I selected the forty- 

 six fish which had spent one winter in the sea, and measured the length of the 

 scales from the centre of growth to the anterior edge of the same, and also 

 the length from the centre to the boundary of the central portion of the 

 scales formed in the river before migration to the sea. By means of the 



* In some fresh-water trout I have measured the total length of the fish, and also 

 the length of the scale-covered portion of the body, reckoning from the angle formed 

 where the gill-cover leaves the cranium. By dividing the total length of the fish by the 

 length of the scale-covered portion I obtain a coefficient denoting the relative dimensions 

 of the two measurements. If no alterations take place in the relative proportions of 

 these two measurements this coefficient would (excluding errors) be constant in fish of 

 all sizes. 



