488 HEREDITY AND SEX 



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 

 one to conclude that every germ-cell whether ovum or sper- 

 matozoon 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 alteration of the ratio between nucleoplasm and 

 cytoplasm, perhaps the introduction of a specific qualitative 

 sex-determinant in fertilisation, which decides whether the 

 organism will become a male or a female and whether masculine 

 or feminine hereditary characters will find expression. 



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 experiments of such a careful worker as Richard Hertwig 

 incline one to keep the question open, though O. Schultze's results 

 seem to close it in one case at least. He experimented with 

 enormous numbers of mice", which are very 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 unaffected by the age of the 

 parents, by apparent vigour, by consanguineous unions, by 

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



7. Third Theory : That the sex is fixed at a very early stage 

 by the constitution of the germ-cells as such, there being 

 female-producing and male-producing germ-cells, pre-deter- 

 mined from the beginning and arising independently of en- 

 vironmental influence. 



On this view there are two kinds of germ-cells, constitu- 

 tionally pre-determined to be female-producers or male-pro- 

 ducers. This implies that the sex is determined before fertilisa- 



