208 



Part III. — Eighteenth Annual Report 



Cunningham shows that they are to be also found, though much less 

 frequently, in the females. It is given by Duncker and Cunningham, 

 however, as a secondary sexual character, although it may be associated 

 rather with some peculiarity in the environment, because it seems to 

 occur more frequently in the Baltic plaice than in those of the Xorth Sea. 



Other secondary sexual differences found by Duncker and Cunningham 

 lay in the height of the body, length of the head, and number of 

 vertebrae and fin-rays. The conclusions of Duncker were, however, incon- 

 clusive,* because of the small number of specimens that he worked with, 

 and because the majority were immature. The differences due to growth, 

 therefore, are not clearly separated from those of sex. Cunningham's 

 conclusions labour under the latter difficulty also, and they are even more 

 unsatisfactory, because he did not calculate the averages. 



The various characters examined by these observers may be gone over 

 in detail. 



Vertebrce and Fin-rays. — These have been examined for sexual 

 differences without result. One example only need be taken. In the 

 adjoining Table IV. the frequencies of the dorsal fin-rays in both sexes 

 and in different regions are given in full, the averages of each are given 

 in the fourth column, and the fluctuations of the total averages are stated 

 at the foot. 



A glance at the averages will show that they are on the whole slightly 

 larger for the males than the females — a result in contradiction to 

 Cunningham's conclusion, but that the fluctuations of the total averages 

 overlap and agree more than they disagree. The conclusion is, therefore, 

 forced upon us that we cannot find any secondary sexual differences in the 

 dorsal fin-rays. In a short preliminary note of his work on the varia- 

 bility of the flounder, Dunckert shows the same result for all the fins. 



The vertebrae and other fins examined by myself lead to the like 

 conclusion, and in their work on the herring both Matthews:}: and 

 Heincke§ found the same thing. It is allowable, therefore, to take the 

 males and females together so far as regards the numbers of vertebrae 

 and fin-rays. 



* See criticism of Duncker's work by F. B. Stead. Jour. Mar. Biol. Ass., Vol. IV.. p. 

 293. 



t Jour. Mar. Biol Ass.. Vol. V., 1898, pp. 172-175. 



t Matthews J. D. : S.F.B. Rep., IV., p. Gl ; V., p. 295. 



§ Heincke, P., I.e. 



[Table. 



