448 INTERNAL SECRETIONS 



The possibility of feminization and masculinization by 

 heterosexual transplantation in birds and mammals has been 

 placed beyond any doubt. The fact of sex being characterized 

 by an ' X '-chromosome is contrary to our hypothesis of the 

 identity of male and female somatic cells before differentiation ; 

 and thus facts seem to stand against facts ! Since a change in 

 the direction of the somatic development can be induced 

 experimentally by the intermediation of hormones, the question 

 arises as to how this fact can be brought into line \\dth the 

 conception of sex chromosomes. Further, the question arises 

 as to what happens to the chromosomes of the somatic cells 

 when a change of sex characters takes place during extrauterine 

 life in insects, birds and mammals. To these questions no 

 satisfactory answer has as yet been given. 



B. DETERMINATION OF SEX. 



When discussing in the foregoing section the influence 

 exerted by the sex glands on the morphogenetic processes in 

 the organism, we put aside the questions as to the factors which 

 are responsible for the determination of sex, and the time 

 at which determination takes place. 



There are two possibilities: Sex may be determined at or 

 even before fertilization ; sex may be determined after fertiliza- 

 tion, i.e., during embryonic development following fertilization. 

 Various external factors are able, as has been shown experi- 

 mentally, to affect the sex-ratio, and it is thought that external 

 factors may normally determine sex. It is of interest to 

 examine the bearing of this question on the hypothesis 

 of an asexual or equipotential embryonic soma, the sexual 

 differentiation of which depends upon sex hormones. 



It is clear that our hypothesis is in full accord with the 

 second suggestion. One might suppose that external factors 

 influence the development of the endocrine sex gland, and 

 thereby determine the sex not only of the latter, but of the 

 soma as well. But there are a great many experiments showing 

 that sex in mammals is already determined at or before 

 fertilization. Is it possible to bring our hj^pothesis on the 

 asexuality of the embryonic soma into line with these facts ? I 

 think that this can be done. If the sex of the fertilized egg is 

 already determined, we must assume that biochemical differ- 

 ences exist between a male and a female fertilized egg. If, 



