6Ö 



of mucli greater salinity. Whereas fishermen and dealers in her- 

 rings linow liow to distinguish these two herrings , and several 

 others also, at first sight, before Heiuclce no naturalist suc- 

 ceeded in this. He began hy comparing herrings with one ano- 

 ther in four respects only ; and as the conclusions obtained in 

 this way were only found confirmed when comparisou was 

 afterwards extended to numerous other characteristic raarks , I 

 resolved to limit myself in my investigations to these four pecu- 

 liarities ^). 



They are: the distance from the apex of the head to the be- 

 ginning of the dorsal fin , from the same point to the origin of 

 the' ventral fin, and to the anal aperture; and in the fourth 

 place the length of the anal fin. With the aid of these four di- 

 mensions, provided that they are applied to very numerous spe- 

 cimens, it is possible to characterise a herring race. The compa- 

 rison of numerous specimens is necessary, because otherwise an 

 individual variation might play a too important part. 



To compare the said dimensions of numerous specimens of fish 

 with one another , Heincke's method always considers them in 

 relation to the length of the fish. The index of any dimension 

 is the quotiënt , resulting from the divisiou of tlie length of the 

 whole fish by the said dimension. On comparing numerous her- 

 rings from various seas with one another it was found that: 



the index of the position of the dorsal fiu varied between 2.08 and 2.47. 



„ „ „ „ „ „ „ ventral fin „ „ 1.97 and 2.28. 



„ „ „ „ „ „ „ anal aperture „ „ 1.41 and 1.65. 



„ „ „ „ length of the anal fin „ „ 12.5 and 7.5. 



To make the comparison easier the indices of the dorsal fin 

 are divided in four groups , which are represented by the ciphers 

 1, 2, 3 and 4 : 1 is used in all those cases in which the dor- 

 sal fin-index is between 2.08 and 2.17, 2 when it is between 



1) In this part of my paper I have not foliowed the original text (in Dutch) of my 

 report; though the conclusions in the main staid the same I preferred to write it 

 down agaia, as my experience with regard to the auturan herring of the Zuiderzee of 

 late has considerably increased and in the second place, as I wished to insert in this 

 paper those facts and consideratioas also, which for practical reasons found a place in 

 one of the appendices of the original report. 



