INTERSEXUALITY 405 



intersexuality. For this purpose we need a classification in 

 which particular characters accessible to direct observation are 

 emphasized. Such a classification cannot, indeed, be a very 

 profound one; but it is necessary to have it. The particular 

 characters which should serve as the basis for such a classifica- 

 tion are the sex characters, and the cases of intersexuality would 

 be here classified according to whether the appearance of 

 these characters is simultaneous, successive, temporary or 

 periodic. 



Accordingly I have proposed two schemes of classification : — 



A . Classification according to sexual hormones. 



1. Simultaneous intersexuality. 



(a) Male and female hormones act simultaneously during 

 embryonic development. Afterwards an establishment 

 of a seemingly normal hormone-production may take 

 place. 



(h) Male and female sexual hormones act simultaneously 

 during the whole of life. 



2. Successive intersexuality. 



{a) Heterologous sexual hormones enter into play during 

 embryonic development. A change to a seemingly 

 normal hormone-production or to simultaneous inter- 

 sexuality is possible. 



(h) Heterologous sexual hormones enter into play during 

 extrauterine life. 



(i) The heterologous sexual hormones remain active 

 for the whole of life. A change to normal hormone- 

 production or to simultaneous intersexuality is 

 possible, 

 (ii) Heterologous sexual hormones remain active 



only temporarily. 

 (iii) Heterologous sexual hormones enter into play 

 periodically. 

 The above scheme is only a further development of the 

 following hypothetical thesis : — 



Intersexuality in the vertebrates is caused by intersexuality in 

 hormone-production, hormones of both sexes acting simultaneously 

 or successively in the same individual. 



