268 THE VARIATION, llACES AND MIGRATIONS OF THE MACKEREL. 



Mariou's kindness, I am inclined to agree with Steindachner in the 

 matter. In any case, there is a marked difference in the number of 

 finrays characteristic of the common and the Spanish mackerel, the 

 two best known species of the genus Scomber. If there are any 

 separate races of the common mackerel, there exists, accordingly, an 

 a 2^^'iori probability that the distinction between these races will 

 include differences in regard to the number of rays in the first dorsal 

 fin, especially as the variability of this character in S. scomler is 

 already known to be considerable. 



Before proceeding to an examination of my results, I should state 

 that the determination of the exact number of rays present in the 

 first dorsal fin of any mackerel is a matter requiring considerable care, 

 owing to the minuteness of the posterior rays. The second or third 

 ray is usually the longest, and the length of the remaining rays 

 decreases gradually to zero. If one wished to omit the minute hinder 

 rays from consideration, it would be as difficult to determine a just 

 arbitrary limit as to endeavour to count the entire series. I have 

 therefore adopted the latter course, and my figures represent the 

 maximum number of finrays recognisable in each fish without actual 

 maceration. 



Upon a first inspection of the figures representing the average 

 number of rays in the fish from each locality, I feared, from their 

 apparent irregularity, that the difficulties of exact determination had 

 proved too great for the acquisition of definite results, and this remark 

 was made in the preliminary account of my researches communicated 

 to the British Association at Bristol. From the" more complete analysis 

 of the figures, however, which I now provide, it will be seen that my 

 fears were groundless, for the data have proved to be of sufficient 

 exactitude to establish an unexpected but convincing relation between 

 number of finrays and size of fish. 



§ 1. General variation. The distribution of finray values among the 

 various consignments of mackerel examined is given in Table E. 



The range of variation is shown to be from a minimum of 9 rays to 

 a maximum of 16 rays, but in a total number of more than 1600 fish 

 the former value was only found twice and the latter value only once. 

 The most frequent value was 12, which was found in about half the 

 fish examined ; 13 rays were found in about one quarter of the fish, 

 and the remaining quarter consisted principally of fish ppssessing 11 

 and 14 rays, the former value being much more frequent than the 

 latter. The fish with 9, 10, 15, and 16 rays formed a very small 

 percentage of the whole (about 3 % altogether). 



§ 2. Local differences. In a sample of 100 fish from the French coast 

 near Jirest, the variation of finray values was absolutely symmetrical 



