2l8 



AN INTRODUCTION TO MODERN GENETICS 



The development of each organ is partly male and partly female. 

 Closer investigation showed that the intersexes were of two types, 

 males transformed towards females, and females transformed towards 

 males. In the former type, the male intersexes, the first formed organs 

 or parts of organs are purely male in type, while the later formed ones 

 are female. Thus the phenotypic sex mosaic is really a time mosaic, a 

 result of early male and later female development. The same thing 

 holds, mutatis mutandis, for female intersexes. The time in develop- 



T IME 



Fig. 101. Intersexuality and the "Switch-over." — The curves show the 

 production of female substance (full line) by all individuals under the control 



of the cytoplasmic [fJ factor, and of the male substance (dotted and dashed 



lines) under the control of NN in males and M in females. A conditions in the 



normal sexes; 6 vsrith female intersexuality [M comes above VVx j ; C with male 



intersexuality ( [ F j comes above MMj. The "switch-over" points are indicated 



by arrows. 



(After Goldschmidt. 



ment when the change from male to female development occurs is the 

 "Drehpunkt" or switch-over.^ 



The sex factors M and F can be supposed to produce substances 

 which control the underlying alternative development-potencies of the 

 tissues in such a way that the tissues develop in either a male or a 

 female direction according as the male or the female substance is in 

 excess. We can make a diagrammatic representation of the production 

 of these substances, plotted against developmental age. A transformed 

 female intersex will show the curve for the female substance at first 

 above that for male substance, but gradually overtaken and surpassed 

 by it, the point of intersection of the two curves being the switch-over. 



The grade of intersexuality can be measured by the time at which 

 the switch-over occurs; thus, with a certain female factor, a strong 



* For criticism of the theory see Baltzer 1937, and reply of Goldschmidt 1938a. 



