FERTILISATION IS DECISIVE 487 



will tend to produce a female. An older egg tends to produce 

 a male. The bias of the ovum may be corroborated or con- 

 tradicted by the condition of the fertilising spermatozoon. 



As the outcome of a very large series of experiments, 

 Prof. Richard Hertwig found that either over-ripeness or 

 under-ripeness of the eggs (due to artificially delaying or hasten- 

 ing fertilisation) led to a large excess of males. Elaborate experi- 

 ments by Sergius Kuschakewitsch have corroborated Hertwig's 

 results up to the hilt. The proportion of males is largely depen- 

 dent on the degree of over-ripeness in the ova, and cultures of 

 males only — with only 4-6 per cent, of deaths — were obtained. 



In connection with fertilisation we may notice a theory 

 that has been suggested by Prof. H. E. Ziegler. He assumes 

 that the chromosomes derived from a grandmother tend to 

 produce a female, and those derived from a grandfather tend 

 to produce a male. He points out that the parental chromo- 

 somes include contributions from grandfather and grandmother, 

 and since the relative numbers of these depend on the chances of 

 the reduction division in maturation, it will be a " toss-up " 

 whether grandfatherly or grandmotherly chromosomes pre- 

 dominate. If the former, the child will be a boy ; if the latter, 

 a girl. 



Suppose the potential offspring has 12 chromosomes from the 

 father and 12 from the mother, as in the human species. If 

 amongst the former there are 8 grandmother chromosomes and 

 amongst the latter 7 grandmother chromosomes, the child will be 

 a girl, for there are at least 15 of the 24 derived from the grand- 

 mother's side. 



Probably, however, this speculation is inadmissible. We 

 must rid our minds of the view (held by many in the past) that 

 there is in ordinary cases any necessary intrinsic bias in the egg 

 to produce a female, any necessary intrinsic bias in the sper- 

 matozoon to incite the development of a male, and that there 

 is thus a combination of maleness and femaleness in the fertilised 



