FACTORS IN SEX-DETERMINATION 487 



somatic stimuli now to one side and now to the other. We 

 beheve that this quantitative fluctuation is a primary character- 

 istic of living units ; a summation of quantitative fluctuations 

 may eventually result in a qualitative bias towards maleness or 

 femaleness in development. 



(&) It may be that the sex is not fixed until fertilisation has 

 been accomplished, for it is conceivable that a predisposition in 

 the young ovum towards becoming a female organism might be 

 counteracted or reversed by a more prepotent spermatozoon 

 which had a protoplasmic predisposition towards becoming a 

 male organism. 



We think that there is a great deal to be said for the hypothesis 

 that the cytoplasm, as distinguished from the chromosomes, is 

 of great importance in sex-determination, by setting up a par- 

 ticular regime of metabolism which makes for the production of 

 a female or a male, and which liberates or inhibits the deter- 

 minants of feminine or masculine structures. At the same time 

 it is conceivable that there may be some kind of germinal struggle 

 between analogous feminine and masculine determinants, and 

 that the issue of this struggle decides whether the masculine or 

 the feminine determinants are to find expression in development 

 or are to remain latent. 



In the case of the insect Protenor helfragi, investigated by 

 Prof. E. B. Wilson, the female insect has in its body-cells one 

 more chromosome than the male has in its body-cells, and some of 

 the spermatozoa have this extra chromosome while others have 

 not. When the e^g is fertilised by a spermatozoon with the 

 same number of chromosomes as itself, it develops into a female. 

 When the e^g is fertilised by a spermatozoon with one chromo- 

 some less than the egg has, it develops into a male. Without 

 in the meantime attaching great importance to this discovery, 

 which we have stated somewhat roughly, we may admit that this 

 inequality of chromosome equipment between the two kinds of 

 spermatozoa may play some role in sex-determination. 



