38 TADACHIKA MINOURA 



In several male-type embryos — nos. 27-6, 43-3, 2-5, 17-1, 

 17-5, and 44-2 — a black pigmentation was present in the gonads. 

 It is a curious and interesting fact that in every case except no. 

 27-6, the black pigmentation is on the left gonad, and in every 

 case it is on the anterior portion of the gonad. In number 27-6 

 the right gonad is also pigmented, but to a much less degree 

 than the left one. I am unable to suggest any explanation of the 

 significance of the pigmentation. Normal testes and ovaries 

 are, of course, never pigmented. Bond ('14) and Pezard ('18) 

 described the occurrence of pigmentation in the ovary of the 

 pheasant in correlation with degenerating processes. In two 

 cases of non-gonad grafts, one case wdth spleen and the other 

 with liver, I found an exactly similar pigmentation of the left 

 testis. It would therefore appear that this occurrence is not a 

 specific effect of the sex hormones. 



Although I have not a large number of cases and although the 

 analysis of the results must in the nature of the experiments 

 be largely of an inferential kind, I believe that these results 

 furnish strong evidence that the sexual characters are reversible 

 and that these characters after having differentiated to a certain 

 extent in the direction of one sex may be altered and modified 

 in the direction of the opposite sex. 



g. Conclusion. Consideration of the experimental data leads 

 us to the following conclusion. The testis and ovary of the chick 

 secrete certain physiological substances, which we may designate 

 sex-hormones. When these secretions are introduced into the 

 body of an embryo they exercise a specific effect upon its repro- 

 ductive system. The development and differentiation of one 

 sex is stimulated by the secretion of the gonad of the same sex 

 and inhibited by the secretion of the gonad of the opposite sex. 

 By means of these secretions, the differentiation of sex in the 

 chick can be controlled to some extent. It may furthermore be 

 stated that the two sexes bear a quantitative and not a qualita- 

 tive relation to each other. 



