of the Fishery Board for Scotland. 



229 



This is not, however, the case, and the example given tends rather to 

 confirm our faith in the method than to destroy it. By means of the 

 method we are able at once to see where conclusions cannot be drawn, 

 and to give good reasons for not doing so. In the other characters, 

 however, where the variability is not so great, there will not be such 

 changes in the averages from year to year. Again, the fluctuations of the 

 averages, which are calculated from the index of variability, leave room 

 for the possible change in the average. 



This objection which mightj be raised simply lays stress on the 

 necessity of comparing, first of all, the individuals of the same generation — 

 i.e., of eliminating the growth-variability, and then of comparing 

 successive generations in order to see if the differences are permanent— 

 before stating definitely that groups or races exist. 



Body-height. — It has been shown that no sex- or growth-variability can 

 be ascribed to this character, and the specimens from the southerly North 

 Sea might all be grouped together and similarly all those from the 

 northerly North Sea. In Table XL, however, the sexes and the different 

 sizes are retained separate, because what applies to any one set is applic- 

 able to the other. 



Cunningham stated that the body-height was distinctly greater in the 

 northern samples than in the southern, and the adjoined Table shows 

 that such is really the case. Whichever groups we compare, male or 

 female, mature or immature, we find the same conclusion. The average 

 of the differences between five groups is 3*91 °/ 00 , and between none of 

 the groups do the fluctuations of the averages overlap. The average 

 body-height for the southerly North Sea is a little over 61°/ 00 of the 

 body-length, whilst that of the northerly North Sea is a little over 65°/ 00 

 of the same length. Reducing the observed difference between the two 

 groups to the percentage of the total length of the fish, we find that the 

 northerly North Sea specimens are higher (or broader) by 2*6 % 0 than the 

 southerly North Sea specimens. This means that a plaice from the 

 former region at 300mm. is greater by T'Smm., or more than a third of 

 an inch, than one from the latter region of the same size, and a plaice at 

 400mm. greater by 10 '4mm., or nearly half an inch. 



The average body-height of a small number of specimens from the 

 Baltic is included in the Table for the sake of a comparison. Although 

 there is no great certainty in the conclusion, the body-height of these is 

 less than that of the northerly North Sea specimens, and approaches more 

 nearly the average body-height for the southerly North Sea. This con- 

 clusion was also arrived at by Duncker. He found that the specimens 

 from Heligoland were slightly smaller than those from the Baltic in this 

 respect, and the latter, again, were considerably smaller than those from 

 the Kattegat. And his conclusions, although he did not make allowances 

 for growth-variability, are perfectly valid, because, as has been shown 

 here, there is no alteration in this character during growth. 



[Table. 



