36 Mr. W. Heape. Proportion of the Sexes produced [Sept. 30, 



autumn shortly after a sudden change from great heat to cooler weather, the 

 other in the early months of the year at a time when the cool winter weather 

 gives place to spring. The increased reproductive activity of the people is 

 suddenly acquired and almost as abruptly allayed, it is obviously not a 

 definite temperature but the experience of a change of temperature which 

 induces this boisterous generative activity. 



The same conditions are found to influence, in a similar manner, other 

 animals which experience breeding seasons, and the effect on stock is 

 increased metabolic activity. There can be no doubt these breeding seasons 

 of the two races in Cuba are brought about by forces which tend to greatly 

 increase the metabolic activity of the individual. 



5. The Effect of the Breeding Seasons on the Proportion of the Sexes produced. 

 — If, then, I am right in stating that the breeding seasons are induced in 

 consequence of increased metabolic activity, and if my reasoning is sound 

 regarding the increased output of F. among illegitimate births and the 

 influence of different degrees of metabolism on the ripening and production 

 of ovarian ova of different sexes, the result of the breeding seasons should 

 show this. 



It does show it, emphatically ; my tables demonstrate that the greatest 

 excess of F. is produced at times of greatest fertility, i.e. during the breeding 

 seasons, when tbe metabolism of the mother is most active. This is true for 

 both races and it is clearly shown in all totals and in the totals for each 

 individual month, except for two months of one year for coloured people. 



I feel convinced such a variation in the sex ratio cannot be ascribed to the 

 action of any law of heredity ; it is clearly associated with the exercise of 

 extraneous forces on the ovary and is, I submit, due to those forces. 



6. The Limitation of the Influence of Extraneous Forces. — In connection 

 with the above, another fact is shown which is of considerable interest, 

 namely, that while whites show a more marked sensibility to the influences 

 which induce the production of F, coloured people are more affected by the 

 forces which stimulate the production of M., and this condition is more 

 marked among illegitimate than among legitimate birth records. 



This fact shows that the race which normally produces a considerable 

 excess of M. is most amenable to the forces which induce the ripening of 

 F. ova, while the race which produces the greatest proportion of F. reacts 

 more generously to the influences which favour the production of M. ova. 

 In other words, there is here demonstrated the exercise of a force which 

 limits the power to produce an excess of either sex, a force which makes 

 for some point near equality of the sexes^ and which is, I take it, the force 

 of heredity. ; 



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