146 Transactions of the Society. 



older the offspring are preponderatingly male, and vice versa. In 

 short, the sex of the offspring tends to be that of the older parent. 

 This has not been confirmed, and Schultze's experiments tell strongly 

 against it. 



Yet it seems fair to notice, that if the germ-cells remain for 

 some time undetermined in regard to the sex which they will ex- 

 press — in other words, if they retain for some time the potentiality 

 of either — there is no a priori reason against the theory that the 

 absolute and relative ages of the parents may have influence. 



Or, again, even if the ova and spermatozoa are, from their first 

 appearance as such, determined towards female-production or to- 

 wards male-production, the age of the parent may favour the 

 production of one kind rather than of the other, or may favour the 

 survival of one kind rather than of the other. 



10. It is hazardous for the inexpert to draw conclusions from 

 statistics, but there seems evidence in mankind of a correlation 

 between the age of the mother and the sex of the child. The 

 younger mothers have more female children ; the older mothers 

 have more male children. On this the self-regulating balance of 

 sex in a nation depends. When females are scarce — for instance, 

 in a colony — they mate early, and supply the demand for girls. 

 When men are scarce — for instance, after war — there are more 

 late marriages, and therefore more boys.* 



11. By many authors, e.g. Girou, and at various dates, the 

 theory has been propounded that the sex of the offspring tends to 

 be that of the more vigorous parent. This is a favourite opinion 

 among breeders and among the fathers of many boys, but it lacks 

 substantiation, and the concept of comparative vigour is too vague 

 to be useful. 



So far as parental vigour may depend on what may be called 

 strained reproduction, or on deterioration supposed to result from 

 close in-breeding, Schultze's experiments on mice do not in the 

 least confirm the view that it has any effect on the proportions of 

 the sexes. 



Starkweather was responsible for the theory that the sex of the 

 offspring tends to be the opposite of that of the superior parent ; 

 but there do not seem to be any secure facts warranting the idea 

 that a prepotent sire has any influence on the sex of the offspring, 

 giving them a bias either towards his own sex or towards the 

 opposite. 



11a. Van Lint maintains that the offspring has the sex of the 

 sexually weaker parent, i.e. the parent whose sex-cells are relatively 

 the weaker at the time of fertilization. If a relatively feeble ovum 

 is fertilized by a relatively vigorous spermatozoon, the embryo will 

 be a female, but its body will follow the father. The author 



* See R. J. Ewart, Nature, Jan. 5, 1911. 



