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logical investigations, viz; that all European and North-African eels, whether found 

 on the coasts of the Atlantic, the Norwegian Sea, the North Sea, the Baltic, or the 

 Mediterranean, have their origin in the spawning grounds of the Atlantic ocean. 



We thus find that the results obtained by biological methods are in excellent 

 agreement with those arrived at by means 

 of the statistical method. 



As regards the direct anti primary 

 cause of this difference between the local 

 stocks of Zoarces on the one hand and 

 all European and American eels on the 

 other, this cannot at present be fully and 

 finally determined. The problem may 

 be formulated as follows: 



Is the fact, that the stock of Zoarces 

 in one locality differs from that of another 

 with regard to average values for number 

 of vertebrae etc., due to genotypic dif- 

 ferences in such two communities, or merely 

 to the effect of varying external con- 

 ditions, or possibly to a combination of 

 both factors? 



This question, which is one of gieat 

 importance from a biological point of 

 view, can hardly be solved without ex- 

 perimental investigations. I do not pur- 

 pose to discuss this point further at pres- 

 ent, more particularly as we hope, during 

 the next few years, to furnish some ex- 

 perimental contribution to the solution of 

 the problem; I have, however, thought it 

 advisable here to advance some few fads 

 from the great mass of observations al- 

 ready made in the course of our inves- 

 tigations, as tending to show that external 

 factors do exert a certain influence upon 

 the average values for the characters of 

 Zoarces. 



We find, for instance, on comparing 

 the number of vertebrae in samples of Zoarces from the inner waters of a fjord 

 with the corresponding value for specimens taken at the mouth, that the figure 

 in question is always lower in the former locality than in the latter. 



This may be seen from Fig. 4, which gives a graphical illustration of the 

 number of vertebrae in two samples, one from the mouth of Manager Fjord, on 

 the East Coast of Jutland (Cattegat) the other from the inner waters of the same 

 fjord. In view of the slight distance between the two localities (about 15. miles 



Fig. 4. No. of vertebrae in a samples of 7,oarces 

 uiinparns from one and the same Danish fjord. 



Graphical view. 

 The upper curve represents a sample from the 

 mouth of Marianer Fjord (East Coast of Jutland, 

 on the Cattegal), the lower one from the inner 



waters of the same fjord. 

 The figures along the vertical line indicate no. of 

 vertebrae. A horizontal interval of 30 mm re- 

 presents 25 specimens. 



