1908.] 



by Whites and Coloured Peoples in Cuba. 



37 



This exemplifies the nature of the claim I made ; extraneous forces 

 undoubtedly exist which effect a variation in the sex ratio, but they are 

 to some extent subordinate to laws of heredity ; nevertheless these former 

 forces cannot be ignored, they are certain to interfere to some extent with 

 the performance of the laws of heredity and with all calculations regarding 

 sex ratio which are based solely upon those laws. 



7. The Effect of Town as compared with Country Life on the Sex Ratio. — 

 Finally, on analysis, my figures show another fact, namely, that a quite con- 

 siderably higher proportion of F. are born in towns than in the country 

 districts. This is shown in my tables for both races and is evident as a rule 

 in the records for both legitimate and illegitimate births. 



I have elsewhere discussed the reason for this ; it is quite clear no law of 

 heredity can explain such a variation, and I have concluded that • the 

 extraneous forces which are accountable for it must again be associated 

 with the degree of metabolic activity experienced by the mother under 

 variable conditions. 



8. Conclusion. — Other facts of considerable interest in relation to this 

 work are set forth elsewhere and I will not refer to them here. I have 

 given above three instances of conditions under which the production of 

 M. and F. children shows a marked variation from the normal. The results 

 are similar for both the whites and the coloured races in Cuba. These 

 people have hereditary qualifications which, in the main, govern the 

 proportion of the sexes they produce, but conditions undoubtedly occur 

 under the influence of which that proportion is varied. This variation is 

 similar in character but different in degree for the two races, and is directly 

 associated with definite extraneous forces, food and climate, which affect the 

 metabolic activity of the mother. 



Taken singly any one of these instances might be thought to be in- 

 conclusive, but taken together they seem to me to present strong evidence 

 of the truth of my contention, that the variable metabolic activity of the 

 mother, acting upon the ovary, induces a struggle for existence between 

 the ovarian ova of different sexes, and affects the proportion of M. or F. ova 

 which ripen and which are produced for fertilisation. 



It is worthy of notice that these same extraneous forces must affect the 

 proportionate produrtion of individuals possessing various kinds of different 

 characters (quite other than sex) which are associated with metabolism, and, 

 when better understood, may have valuable bearing on the means for selection 

 of healthy ova and for preventing the maturation of ova bearing the active 

 germs of disease. 



