68 



PHYSIOLOGICAL GENETICS 



formula, the sexual balance is shifted correspondingly in favor of 

 F. The result is thai an ascending scries of male intersexes ie 

 produced, beginning w itb a combination giving normal male- and 

 Leading through all Btages of low to high intersexuality, finally to 

 sex reversal, i.e., females. The actual result of such a series of 

 replacement experiments is represented in the following table. 



Here we notice the phenomenon that is of interest in the present 

 discussion. If the sexual balance is shifted so that the lowest 

 grade of intersexuality is produced, it does not happen to all 

 individuals but only to a certain percentage, which increases with 

 increasing grade of intersexuality. There is obviously a thres- 

 hold, or limiting value, for F/MM at which intersexuality 

 begins (called the epistatic minimum in this case). And there is 

 obviously a fluctuation of the value F/MM around a mean — 

 whether as a modification or produced by modifying genes is 

 irrelevant — with the consequence that only individuals belonging 

 to the part of the range of variation beyond the threshold become 

 intersexual. (Pictures of such a series of male intersexes are 

 given in Fig. 35, page 194.) The same will be found at the other 

 end of the series, where a high degree of intersexuality fluctuates 

 into femaleness. It might be added that recent discussions of 

 the special problems of sex and intersexuality by Dobzhansky and 

 Goldschmidt (see page 66) have added the possibility that the 

 cytoplasmic factor which is designated as F, because working 

 in the direction of female determination, might in fact be some- 



