The President's Address. By J. Arthur Thomson. 147 



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. The sex of the child settles the question. 

 " Le sexe de l'enfant tranchera la question." The theory lacks 

 scientific backing. 



12. 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 fertilization. Thury and other breeders have main- 

 tained that an ovum fertilized soon after ovulation is likely to 

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

 in any way, e.g. by continuiug to live without feeding, will tend to 

 produce a female. The bias of the ovum may be corroborated or 

 contradicted by the condition of the fertilizing spermatozoon. 



As the outcome of a very large series of experiments, Professor 

 Richard Hertwig found that either over-ripeness or under-ripeness 

 of the eggs (due to artificially delaying or hastening fertilization) 

 led to a large excess of males. Unfortunately, as in the case of 

 Yung's experiments, the cogency of Hertwig's results is lessened 

 by the high mortality of the tadpoles and the possibility that this 

 is differential. 



A side-light is here available from Vernou's experiments on 

 hybridizing sea-urchins, for he found that the offspring of a cross 

 usually exhibited the characters of the parent whose germ-cells 

 were the fresher, the less stale, at the time of fertilization. 



13. From a survey of 200,000 births in Buenos Ayres, Pearl 

 found that the proportion of males is distinctly greater (1 ■ 5 per 

 cent.) when the parents are of different races. 



14. In connexion with fertilization we may notice a theory 

 that has been suggested by Prof. H. E. Ziegler. Let us start with 

 a fertilized ovum whose chromosomes have become fixed towards 

 female development : at a certain stage in the development the 

 reproductive cells are segregated ; let us suppose that they, like 

 the fertilized ovum, have a predisposition to develop into females ; 

 let us suppose that this predisposition is not affected by nutritive 

 oscillations in the body ; let us suppose a similar state of affairs in 

 a male ; and that fertilization occurs. A number of chromosomes, 

 say twelve, in a spermatozoon from the male parent, which tend by 

 hypothesis to be the material basis of male offspring, unite in 

 fertilization with an equal number of chromosomes in an ovum 

 from the female parent, which tend by hypothesis to be the 

 material basis of female offspring, then the fertilized ovum will 

 not be biased towards the production of either sex, as far as its 

 complement of chromosomes is concerned. On this view the 

 proportions of the sexes should be equal, which is often far from 

 being the case. 



Prof. Ziegler's suggestion is that since the parental chromo- 



