526 LIFE : OUTLINES OF GENERAL BIOLOGY 



and certain sign of a man being "sexually more vigorous" than his 

 wife is their having a daughter. "Le sexe de I'enfant tranchera la 

 question." 



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 fertiUsed 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, will tend to produce a 

 female. An older egg tends to produce a male. The bias of the ovum 

 may be corroborated or contradicted by the condition of the 

 fertilising spermatozoon. 



As the outcome of prolonged experiments. Prof. Richard Hertwig 

 found that either over-ripeness or under-ripeness of the eggs (due 

 to artificially delaying or hastening fertihsation) led to a large excess 

 of males. Elaborate experiments by Sergius Kuschakewitsch have 

 corroborated Hertwig's results up to the hilt. The proportion of 

 males is largely dependent on the degree of over-ripeness in the ova, 

 and cultures of fnales only — with only 4-6 per cent, of deaths — 

 were obtained. 



In connection with fertilisation we may notice the theory of 

 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 

 chromosomes include contributions from the grandfather and the 

 grandmother, and since the relative numbcTS of these depend on 

 the chances of the reduction di\ision in maturation, it will be a 

 "toss-up" whether grandfatherly or grandmotherly chromosomes 

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

 girl. 



Suppose the ]X)tcntial offspring has 24 chromosomes from the 

 father and 24 from the mother, as in the human species: If the 

 former include 16 grandmother chromosomes and the latter 14 

 grandmother chromosomes, the child will be a girl, for 30 of the 

 48 chromosomes are derived from the grandmothers' side. 



Probably, however, this speculation is quite inadmissible. We 

 must rid our minds of the view that there is in ordinary cases any 

 necessary intrinsic bias in the egg to produce a female, any necessary 

 intrinsic bias in the spermatozoon to incite the development of a 

 male. 



Our conclusion in regard to the second theory must be: that 

 there is little warrant for attaching much importance to the relative 

 condition of the germ-cells at the time of amphimixis. The experi- 

 ments of such a careful worker as Richard Hertwig incline us to 

 keep the question open, but O. Schultzc's results seem to close it 

 in one case at least. He experimented with enormous numbers of 



