276 THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 



This result is iu complete agreement with the results already obtained 

 in regard to the number of bars and the degree of spottiness. 



That this result is not accidental, but is founded on real differences 

 in the degree of evolution of the different races of fish will be made 

 clear in the next section. 



X. Correlation between Spottiness and Number of Finrays. 



We have already seen that the presence of intermediate spots among 

 the transverse bars indicates a departure from the primitive arrangement 

 of the bars, which coincided with the lines of the myotomes or muscle- 

 segments. Increased spottiness accordingly indicates an increased 

 departure from the primitive condition. We have also seen that the 

 common mackerel belongs to the most primitive group of species of the 

 genus Scomher so far as its markings are concerned. I have, moreover, 

 briefly referred to the fact that the number of finrays in the first dorsal 

 fin is higher in the common mackerel than in any other species of the 

 genus Scomher, As the number of finrays has also been shown to be 

 higher in young than in old mackerel, it is certain that, for the race 

 as for the individual, a high number of (inrays is the primitive condition 

 for Scombroid fishes. 



Accordingly, as increase in spottiness and reduction of finrays are 

 equally departures from the primitive condition, we might expect to 

 find a correlation between these two characters in well-defined races 

 of mackerel ; and if this correlation occurs in representative samples 

 of fishes from different localities, it furnishes the strongest possible 

 argument for their racial distinctness. 



Such a correlation undoubtedly exists, as is shown in the following 

 table, which gives for each group of fishes the indices of spottiness 

 already ascertained (p. 267) side by side with the mean number of 

 finrays in the first dorsal fin, as determined in fish of 13 inches length. 

 Although an extensive examination of the variation of the Spanish 

 mackerel, Scomher colias, has not yet been made, its spottiness is so 

 marked, and the number of its finrays is so decidedly reduced, that 

 I have no hesitation in placing it here as a type of extreme departure 

 from the primitive Scombroid condition. 



