70 INTERNAL SECRETIONS 



uterus develops independently of the gonad. I do not think 

 that Vandel's suggestion is justified; the development of the 

 gonad and that of the copulatory apparatus of the respective 

 sex may both be contoUed by some other factor. 



Contradictory as they are, the observations made on different 

 Invertebrata show that here also somatic sexual characters 

 depend in some cases upon the sexual glands ; this dependence 

 concerns, as we have seen, those parts which are intimately 

 involved in the sexual function. 



G. SUMMARY. 



The facts recorded permit us to answer the questions put in 

 the first chapter: 



1. It is shown with absolute certainty that the formation 

 and the persistence of sexual characters in mammals, birds, 

 amphibians, and some invertebrates depend upon the sexual 

 glands. These sexual characters may be designated as 

 "secondary," in a genetic sense of the word> in relation to the 

 sexual glands. 



2. The formative and conservative influence of the sexual 

 glands does not relate to all the sexual characters. Only some 

 of the sexual characters therefore can be designated as geneti- 

 cally secondary in relation to the sexual glands. 



3. The formative and conservative influence of the sexual 

 glands concerns not only those sexual characters which are 

 involved in the sexual function, such as the genital organs, 

 the characteristics of heat and the psycho-sexual behaviour, 

 but it concerns also sexual characters which seem to be in no 

 special relation to the sexual function, such as the plumage, 

 body proportions, and so on. This formative and conservative 

 influence may even relate to other characters which are not 

 necessarily different in the two sexes, e.g., some of the other 

 organs of internal secretion. 



4. (a) By castration the sexually differentiated type, i.e., 

 the male or the female, loses more or less its sexual characters, 

 and shows a tendency to become a sexually indifferent form 

 common to both sexes. The later castration is performed the 

 greater the number of the sexual characters which remain in 

 the *' castrate." 



