278 THE VAKIATION, llACES AND MIGRATIONS OF THE MACKEKEL. 



Brest and Scilly fish, or that of the partial series of transverse bars 

 (Table C), as by any means decisive. I hope to re-examine these details 

 by means of larger samples during the coming year. 



XI. Second Dorsal Fin. 



The variation in the number of finrays in the second dorsal fin is 

 much slighter than in the case of the first dorsal. The extreme range 

 of variation is from 9 to 15, i.e., 7 rays; but the two extreme values 

 on each side of the mode {i.e., 9, 10, 14, and 15) occur very rarely, 

 so that the range of variation scarcely covers more than 3 rays, viz., 

 from 11 to 13. 



Owing to the limited variability of the organ, no useful purpose 

 would be served by publishing the separate data for the various con- 

 signments of fish, and I have therefore confined myself to a statement 

 of the observed results for each locality as a whole. These are set 

 out in Table G (p. 295). 



There is a marked difference in the variability of this organ in the 

 American fish as compared with the samples of European fish ; for, 

 whereas 12 rays occur in from 82 to 85 % of the European fish, they 

 are found in only 63 °/o of the American, and the frequency of each 

 of the remaining values is from twice to three times as great for the 

 American fish as for the European. The mean value for the American 

 sample is also considerably lower than for any European sample 

 examined. The highest mean is that for the Xorth Sea (11-950), and 

 the lowest that for Kinsale (11-927), the difference between the two 

 being 0023. But the difference between the American mean and the 

 nearest European mean is much greater than this, being 0"077. 



The differences between the European samples are exceedingly slight, 

 but attention may be drawn to the fact that the localities which provide 

 the highest and lowest mean-values are geographically remote, viz., 

 the North Sea and Kinsale. 



The only satisfactory way of comparing values which present such 

 slight local differences in the frequency of their occurrence, will be to 

 combine the values above and below the mode (12) into two com- 

 partments of high and low value respectively, as below. 



