CONSIDERATION OF INDIVIDUAL FISH 



99 



3, Distance of the anus from the tip of the snout. " A " in the 

 Tables. 



4. Length of the base of the anal fin. From the root of the first 

 to the root of the last fin ray of the anal fin. " An " in the Tables. 



From these four measurements Heincke believed that he could 

 distinguish spring from autumn-spawning herring, provided a 

 sufficiently large number of individuals were taken and the average 

 calculated, otherwise the individual variation would be too great. 



The characteristics are always expressed by Heincke as relative 

 and not as absolute measurements, and they are expressed as a 

 ratio of the total length, inclusive of the caudal fin. 



A comparison of a large number of measurements showed that 



1. The distance of the dorsal fin varied from 2-08 to 2-47 



2. „ „ ventral „ 1-97 to 2-28 

 3- .. ,. anus „ 1-41 to 1-65 

 4. The length of the base of the anal fin from 12-5 to 7-5 



In order to make comparisons easier the ratios expressing the 

 distance of the dorsal fin from the tip of the snout are divided into 

 four groups, each of which is distinguished by a number : — 



1. When the ratios varied from 2-08 to 2 •17 



2. „ „ „ „ 2-l8t0 2-27 



3- ., .. ., .. 2-28 to 2-37 



4- .. .. .. .. 2-38 to 2-47 



In a similar manner each of the other ratios was divided into 

 four groups with the exception of the distance of the anus, which 

 was divided into five. To each of these groups descriptive numbers 

 or letters were applied, viz. : — 



Heincke next stated that spring herring could be designated 

 by the formula 2bII and the autumn herring by the formulae 2al 

 or 2aII. 



In the first place it should be noted that the formulae do not 

 express what they are intended to, and that it is quite possible 

 that they can convey false impressions. 



For instance, it is quite possible that two groups of spring herring, 

 to each of which Heincke 's average formula abll applies, are really 



