I "^"*" Mancltestcr Mcinoiis, Vol. Ivii. (igi ^"^j ?.\-i. ?*. 9 



a'vvell-marked difference between the scales of the two 

 kinds of fish, and that this difference is greater than the 

 known difference between scales of the same region in the 

 same fish and greater than a difference due to error of 

 observation, there would be some reason for believing 

 that the two kinds of fish are distinct races. 



Such observations have not been made on an extensive 

 plan, but the researches carried on in the Manchester 

 Universit}- during the past two N-ears are sufficient to 

 prove that such a distinction between the two kinds of 

 fish, if it exists, must be so slight that it can be of very 

 little practical use. 



It should be stated quite clearh-, however, that the 

 results obtained do not disprove the theory that there are 

 two races of salmon. All that is shown is that the 

 difference between the two races is not clearly marked by 

 a difference in the number of the annuli in the scales. 



In spite of the fact that the data as regards the scales 

 do not aid in a consideration of the racial question, there 

 are many very interesting points which can be learnt from 

 them. For instance, if we classify the fish according to 

 the length of time spent in the sea, comparisons can be 

 made between the relative weights and lengths and girths 

 of what have been termed the various kinds of salmon. 

 (See Table 6.) It will be observed that the average 

 weight of the small spring fish is ver)' nearly equal to the 

 average weight of the small summer fish, and the same is 

 true of the large spring and large summer fish. This 

 brings forward the question whether these fish have lengths 

 and girths corresponding to their weights. To answer 

 this the ratios of length and weight and length and girth 

 have been ascertained for each kind of fish and their 

 averages compared. Considering first the averages of 

 the ratios of length and weight, Graphs 3 and 7 indicate 

 that on the whole the fish which have spent a long time 



