486 HEREDITY AND SEX 



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 " superiority " and " comparative vigour " are far 

 too vague to be scientifically discussable. Dr. Marshall notes 

 that Allison, an authority on the thoroughbred horse, accepts 

 Starkweather's theory. So far as we have been able to discover, 

 there are not any secure facts warranting the idea that a pre- 

 potent sire gives his offspring a bias either towards his own sex 

 or towards the opposite. 



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 fertilisation. If a relatively feeble ovum 

 is fertilised by a relatively vigorous spermatozoon, the embryo 

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

 explains under six heads what is meant by being sexually 

 weaker or stronger, but he naively points out that the sure 

 and certain sign of a man's being more sexually vigorous than 

 his wife is his having a daughter. " Le sexe de l'enfant tranchera 

 la question." The theory lacks scientific backing. 



It has been repeatedly suggested that a determining factor 

 may be found in the relative maturity or freshness of the sex- 

 cells which unite in fertilisation. Thury and other breeders have 

 maintained that an ovum fertilised soon after ovulation is likely 

 to produce a female. That is to say, the fresher ovum, not 

 exhausted in any way, e.g. by continuing to live without feeding, 



