31 



In the first instance Heincke made his measurements 

 with regard to four characteristics. Subsequently he 

 extended his observations to include a large number of 

 characters ; he found, nevertheless, that the four characters 

 originally chosen by him gave him the most important 

 results. 



These four characters are: — 



1. Distance of the dorsal fin from the end of the snout. 

 Measured from the end of the snout with the mouth 

 closed, to the root of the first fin ray of the dorsal hn. 

 " D " in Heiucke's Tables 



2. Distance of the ventral fin from the end of the snout. 

 Measured from the end of the snout with the mouth closed 

 to the root of the first fin ray of the ventral fin. " Y " 

 in the Tables. 



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 her- 

 ring, 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 



