THE THEORY OF SEX 599 



normally only the first sex is realized. The experiments on in- 

 tersexuality will show why this is the case. Let us suppose that 

 the fertilized egg of the moth starts development. Growth and 

 differentiation will proceed with a certain rapidity, given con- 

 stant temperature, etc. During development a moment comes 

 for every organ when its differentiation starts and when sexual 

 differences are possible. At this point it must choose one of 

 two alternatives, e.g., the scales of the wing must decide either 

 to form pigment or to be filled with air. This decision must be 

 brought about by the action of the dominating enzyme. And the 

 one present in higher concentration will first succeed in furnish- 

 ing the necessary amount of specific substance acting as deter- 

 miner, which we may call the hormones of male or female dif- 

 ferentiation. In normal sex-determination the relative concen- 

 trations of the andrase and the gynase are so fixed that the de- 

 termination-point for the less concentrated one falls only after 

 the completion of differentiation. The facts reported on the 

 subject of intersexuality, show that when the less concentrated 

 enzyme reaches that turning-point within the limits of embryonic 

 differentiation, it really goes into action. Now one of several 

 things may happen. Both hormones may act together, giving 

 some intermediate sort of result ; or the newcomer may take the 

 action into its own hands — possibly because the supply of the 

 other set of hormones is becoming smaller — and the differentiation 

 assumes, from this moment on, the character of the other sex. 

 The facts prove the latter to be the case. 



If we should now work out the details of the production of 

 the two types of intersexuaUty some difficulties would arise 

 which would have to be explained. But as the more important 

 part of the theory is its general aspect — whereas the details 

 may possibly be conceived in different ways — we shall first 

 show how the facts fit the general theory. 



If the theory is correct, one of the expectations would be that 

 normally every organ of the moth should develop under the ex- 

 clusive influence of the andrase or the gynase. But if we are 



THE JOURNAI, OF EXPERIMENTAL ZOOLOGY, VOL. 22, NO. 3 



