THE VARIATION, RACES AND MIGRATIONS OF THE MACKEREL. 251 



of the points selected. Bateson, for example, speaking of the grey- 

 mullet, says, "Similarity in size seems to be usual in these shoals." 

 (Journal M.B.A., I., p. 250.) If, therefore, we assume this principle in 

 the case of mackerel shoals, it is clear, from the facts to be adduced 

 shortly, that the normal preponderance of females will tend to be 

 reduced in the case of shoals of fish below 14 inches in length, and 

 increased in the case of shoals of fish measuring 15 inches or more, 

 quite independently of any selective segregation of the sexes. 



It is then possibly not without significance that, so far as my own 

 samples go, a preponderance of males was only observed in samples 

 of relatively small fish, more than half the fishes in each sample being 

 below 14 inches in length, and a very small number (from 0% to 11 %) 

 attaining a length of 15 inches. 



§ 3. Seo: and Size. The following table shows the observed frequency 

 of male and female fish of the various sizes mentioned, in a total 

 population of 918 mackerel, and also the same facts as percentages 

 of this latter sum. This population consists of all the samples of 

 British fish in which the sex has been determined, as shown in Table 

 E. The American sample has been excluded, since the present in- 

 vestigation clearly shows the American fish to constitute a distinct race, 

 much more remotely allied to the European fish than are the British 

 races inter sc. The last horizontal row of figures shows the relative 

 number of females of each size compared with the number of males 

 of the same size taken as 100. 



Table III., shoiving relation between Sex and Size. 



The table shows that the females in my samples exceed the males in 

 number at almost every size, the exceptions being at 11 inches where 

 the frequency of males and females is the same, and at 13 inches where 

 the males exceed the females by 1 7o of the total number. It is to 



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