L 48 Transactions of the Society. 



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 predominate. 

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

 mother's side." * 



15. Probably, how r ever, 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 spermatozoon 

 to incite the development of a male, and that there is thus a 

 combination of maleness and femaleness in the fertilized egg. It 

 is enough to recall the fact that the drone-bee has a mother but 

 no father, and the same is true of many Hymenoptera. This is 

 but a striking instance of the numerous facts which lead us to 

 conclude that every germ-cell — whether ovum or spermatozoon — 

 has in it the potentiality of the distinctive characters of both sexes. 

 At some stage or other, as we are discussing, something occurs, 

 perhaps a fixing of the metabolism-rhythm, perhaps some altera- 

 tion of the ratio between nucleoplasm and cytoplasm, perhaps the 

 introduction of a specific qualitative sex-determinant in fertilization, 

 which decides whether the masculine or feminine hereditary char- 

 acters will find expression. 



16. Finally, in reference to the question of the relative condi- 

 tions of the parents at the time of fertilization, we must refer to 

 0. Schultze's prolonged experiments with enormous numbers of 

 mice, which are good subjects, being ready to breed when seven 

 weeks old, and littering it may be every three weeks, if not allowed 

 to suckle. He found that the proportions of the sexes were un- 

 affected by age of parent, by apparent vigour, by consanguineous 

 unions, by frequency of births, or by any kind of nutritive change. 

 And one doubts whether there is much warrant for supposing that 

 the germ-cells come together free from any sex-predestination, or 

 that much importance can be attached to their relative condition 

 at the time of amphimixis. On the other hand, the experiments 

 of such a careful worker as Eichard Hertwig incline one to keep 

 the question open a little longer. The possibility that determin- 

 ation occurs in fertilization when already predestinated germ-cells 

 meet, will be discussed later on. 



* T. H. Morgan, " Experimental Zoology," 1907, p. 419. 



