THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 281 



Table XL, sliovnng frequency of High and Low Numhers 



of Dorsal Finlets. 



(Percentages.) 



This table is, on the whole, similar in its general features to Table X., 

 showing the variation of the second dorsal finrays. A very close 

 affinity is revealed between Kinsale and Kerry, and again between 

 Plymouth and the combined samples from Brest and Scilly, but the 

 North Sea values, which merely approximated to the Irish values in 

 the case of the dorsal iin, now entirely agree with them. 



We again see that the Irish group is characterised by the high 

 frequency of the normal number of finlets, or, as we may say, by its 

 high normality. 



In revealing the close affinity between the Kinsale and Kerry groups, 

 and between the Plymouth group and the combined Brest and Scilly 

 samples, this table furnishes a confirmation of what has previously 

 been urged with regard to these points. The difference between the 

 North Sea and Channel groups, although foreshadowed in the case 

 of the second dorsal fin, is novel, and possibly significant ; but in the 

 next section it is shown that the variability of these organs is too 

 slight to admit of any inferences being safely drawn as to the affinity 

 between the various local groups of fish. The maximum number 

 representing any one locality is only 410, while the deviations from 

 the normal condition do not exceed 8 % for any of the British localities 

 in the case of the dorsal finlets. 



XIII. Correlation between Variations of Second Dorsal Fin 

 AND Number of Dorsal Finlets. 



During the examination of the mackerel received, I frequently had 

 occasion to notice that a marked degree of correlation exists between 

 the number of finrays in the second dorsal fin and the number of finlets. 

 I am not qualified at present to discuss the facts from a mathematical 



