270 THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 



everywhere to exceed the percentage of values below it ; but neither by 

 a comparison of the percentages themselves, nor by the study of the 

 average values for each locality, is it possible to trace any marked 

 evidences of racial distinction among the British fish. The American 

 fish alone seem to possess any distinguishing peculiarity as regards the 

 variation of this organ. 



The question, however, is complicated by the factors of growth and 

 sex. ]\Iatthews has shown that in the herring there is a slight increase 

 in the number of dorsal finrays with the growth of the fish, an increase 

 which is not so much due to the appearance of new rays as to the 

 enlargement of the minute anterior ray, which renders it less liable 

 to escape notice in large fish than in small (4th Eeport Scottish Fishery 

 Board, 1886, p. 92). It is therefore necessary to enquire whether there 

 exists any similar relation in the mackerel between size of fish and 

 number of recognisable rays. 



Moreover, the first dorsal fin is frequently modified as a secondary 

 sexual character in bony fislies, and although no such modification 

 has ever been recognised in the mackerel, it is important to ascertain 

 whetlier or not the number of rays is correlated with sexual distinctions. 

 The proportion of the sexes in the various consignments of fish 

 examined was not always uniform, and, if any correlation exists, the 

 preponderance of opposite sexes in two different samples would occasion 

 a difference in the results which m.ight be readily mistaken for evidence 

 of racial peculiarities. 



§ 3. Number of Finrays according to Sex and Size. The sex of the 

 fishes examined during the autumn of 1897 was not always determined, 

 so that in the present enquiry we shall be restricted to the following 

 samples of fish : — 



Irela^ul. 



(1) Kinsale, July 1st, 1898 



(2) Smerwick, March 12th, 1898 



(3) Brandon, April 16th, 1898 . 



(4) „ „ 23rd „ . 



Total 



44 males and 56 females 

 63 „ „ 36 „ 

 20 2.5 



43 „ „ 58 „ 



170 



175 



English Channel and North Sea. 



(1) Plymouth, Nov. 16th to 20th, 1897 41 males and 59 females 



(2) „ July 6tli, 1898 . . 42 „ „ 58 „ 



(3) „ „ 11th „ . .10 „ „ 14 „ 



(4) Ramsgate, Oct. 27th, 1897 . . 55 „ „ 45 „ 



(5) Lowestoft, Oct. 12th „ . . 15 „ „ 10 „ 



(6) „ June 28th, 1898 . 21 „ „ 29 „ 



(7) „ July 12th „ .39 „ „ 61 



Total . . 223 „ „ 276 





