— 22 — 



eels as a whole and the Anieiùcan in like wise^. And since the two last named 

 are classed as distinct species, Anguilla vulgaris and A. rostrata, it would be equally 

 correct, statistically speaking, to regard for instance, two of the most widely differing 

 stocks of Zoarces as distinct species also. 



With regard to the cause of this homogeneity in all samples of Anguilla vulgaris 

 and of the heterogeneity in the Zoarces samples, there is little room for doubt. The 



v_ 



119 



118- 



117- 



116 



115 



114 



113 



112 



111 



1101- 



109 



108 



107 



106 



105 



104 



Fig. 3. No. of vertebrae in 2 samples of European and American eels. Graphical view. 

 The upper curve represents a sample of European elvers (from Denmark), the lower one of American 



elvers (from Mass. U. S. A.; the same as shown in Table II, p. 6). 

 The figures along the vertical line indicate no. of vertebrae. A horizontal interval of ;iO mm repres- 

 ents 25 specimens. 



difference must be due to the fact that all European eels are of the same 

 origin, whereas the Zoarces exist as separate communities each 

 distinct from the other. And as far as we know, the eel is the most migratory 

 of all our species of fish, while Zoarces is probably the least inclined to migration. 



It is thus seen, how highly the statistical composition of a stock of fish is 

 affected by the biological peculiarities of the species. 



The results of the statistical investigations agree entirely with the results which 

 I had previously obtained in the case of the eel (1906 — 1912) on the basis of bio- 



' With regard to .-1. rostrata, however, one reservation should be made: up to the present, we 

 have not, as in the case of .4. vulgaris, examined a sufficient quantity of samples to determine whether 

 all American eels are identical in this respect. 



