Internal Factors of Sex Determination 405 



would have exactly opposing influences. Apparently the only 

 way out of the dilemma is to assume selective fertilization on the 

 part of the sperm, so that only male-determining spermatozoa 

 (i.e. those without the accessory) can enter eggs containing 

 the male chromosome, and only female-determining (i.e. 

 those with the accessory) can enter eggs containing the fe- 

 male chromosome. Thus the primary assumption forces us to 

 make another one that lacks at present evidence in its support. 

 Moreover, instead of offering us a simple explanation of sex- 

 determination, the hypothesis seems unnecessarily complex, 

 since it postulates that both eggs and sperm are male or female 

 producing, while theoretically the result could be as readily accom- 

 plished by one of them only being male or female producing. 



The complication is primarily due to the assumption that the 

 accessory chromosome is a carrier of female pangenes or bio- 

 phors. If we reject this assumption, we find, I think, a simpler 

 explanation of the influence of the spermatozoon carrying the 

 accessory in determining sex. Suppose we assume that the 

 result is due to the greater amount of chromatin brought 

 into the egg by the sperm with the accessory. It will make 

 no difference on this assumption which one of the homologous 

 accessory chromosomes happens to be present in the egg. The 

 result is parallel to that of the bee, in the sense that the fertilized 

 egg contains more chromosomes than the unfertilized, and pro- 

 duces in consequence the female. In the absence of all knowledge 

 as to how the greater quantity of chromatin produces a female, 

 one is tempted to assume that the result is reached through as- 

 similative changes that take place in the early cells, and there is 

 some evidence in favor of the view that one of the main func- 

 tions of the chromatin is to carry on the assimilative processes 

 in the cells. 



The egg of the bee if fertilized produces a female, if unfer- 

 tilized a male. This relation has led a number of zoologists 

 to conclude that all the eggs are male, but become female on 

 fertilization, since the female element introduced by the sperm 

 dominates the male elements of the egg. The spermatozoa con- 



