OF LIFE IN GENERAL. 321 



fish again showed the widest variation, only 79 per 

 cent, of them having 5 finlets. The Irish fish again 

 showed the smallest variation, 94.4 per cent, of them 

 having 5 finlets, as against 93.6 per cent, in North Sea 

 and Plymouth samples, and 93.0 per cent, in those from 

 Brest and Scilly. 



It is obvious, therefore, that the American mackerel 

 constitute a distinct variety or race, the most notice- 

 able characteristic of which is the high degree of spot- 

 tiness. Garstang is of the opinion, also, that the 

 mackerel which frequent the British coasts should be 

 subdivided into two principal races: an Irish race, and 

 an English Channel and North Sea race. The chief 

 differences between these two subdivisions lie in the 

 number of transverse bars and of spots, and to a lesser 

 degree, of dorsal fin-rays and finlets. It is a striking 

 fact, also, that " these peculiarities are greatest between 

 the races of localities which are geographically remote, 

 and least between those which occupy areas that are 

 geographically contiguous. Between the mackerel of 

 the North Sea and English Channel there are no dif- 

 ferences at all; but the Irish race is distinctly divisible 

 into two stocks, one of which is restricted to the west 

 coast, and the other to the south." 



Into the causes of the variations shown by these local 

 races Garstang does not enter. It is highly improba- 

 ble that all of the observed differences are the direct 

 or indirect result of differences of environment, but it 

 is possible that some of them, such as the bars and 

 spots, and size of the fish (and with_ this the number 

 of dorsal fin-rays), may be considerably influenced 

 thereby. 



