284 THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 



ground of the close resemblance they exhibit in regard to the high 

 mean number of linlets, the resulting mean for the finlets becomes 

 5-015, and that for the fiurays 11-948. Each of these values would he 

 the hii/hest in its series, and therefore hopelessly wrong from the point 

 of view of correlation. 



Similarly, if the Plymouth and Kinsale groups are amalgamated, the 

 resulting means would both be among the lowest in their respective 

 series, instead of displaying the inverse relation of high and low values 

 which is demanded for accuracy. 



I conclude from these facts that the grouping which fulfils the 

 correlation test is the correct one; and, as this grouping is identical 

 with that demanded by the variation of all the other characters 

 examined, it would appear to rest upon the firm basis of real genetic 

 affinity and racial differences. 



XIV. Summary of Evidence concerning the Eaces of the 



Mackerel, 



§ 1. American Mackerel, 



The American mackerel have been shown in this report to differ very 

 considerably from all samples of European mackerel examined. 



The difference is exhibited in regard to every character the variation 

 of which has been determined, and in every respect the American fish 

 hold an extreme position among my samples. Thus the highest average 

 is yielded by the American sample in regard to the following characters: 

 (1) the number of transverse bars, (2) the number of spotty fish, (3) 

 the number of spots per hundred fish, and (4) the number of dorsal 

 finlets; whilst the lowest average is yielded by it in regard to the 

 number of finrays in (1) the first dorsal, and (2) the second dorsal fin. 



There can be no doubt as to the significance of these facts. The 

 American mackerel constitute a distinct variety or race, whose most 

 obvious characteristic is its high degree of spottiness. 



It must remain for American or Canadian naturalists to determine 

 the question as to the existence of minor local differences among the 

 American fish. During the meeting of the British Association at 

 Toronto last year, I examined a dozen mackerel which had been caught 

 in the Gulf of St. Lawrence; and, although this number is insufficient 

 to determine the existence of minute racial differences, I may state that 

 it was the examination of these fish which first revealed to me the 

 marked spottiness of the mackerel of the western shores of the Atlantic. 

 In this respect, therefore, I have no doubt of the close agreement 

 between the mackerel of Canadian and American waters. 



