32 TADACHIKA MINOURA 



DISCUSSION 



a. Action of sex horrnones. The experiments presented in 

 this paper show that the primary sexual characters of the chick 

 embryo can be altered in several different waj-s through the 

 implantation of testis and ovary tissue on the membranes of the 

 embryo. Various degrees of intersexuality were produced. 

 Whenever affected embryos resulted, it was always found that 

 the grafts were growing (or had grown) and that a vascular con- 

 nection had been established between the graft and the embryonic 

 circulation. It is therefore not only a reasonable, but an unavoid- 

 able conclusion that the effect produced by the grafts on the 

 embryo must have occurred by way of the circulation. It may 

 indeed be conclusively stated that the grafts produced sub- 

 stances which were carried to the embryo in the blood stream 

 and modified its sexual differentiation. 



It may therefore be regarded as demonstrated that the gonads 

 secrete substances which may be designated sex-hormones, 

 which control or modify both primary and secondary sexual 

 characters. The experimental work presented in this paper is 

 in complete accord with Lillie's explanation of the free-martin 

 condition in cattle, namely, that the free-martin is a female 

 whose primary sexual characters have been modified in the male 

 direction by the action of hormones originating in the testes of 

 the male cotwin. My work shows that testicular and ovarian 

 secretions actually do have such modifying effects on the primary 

 sexual characters. 



b. Specific function. It is necessary to determine whether or 

 not the modifications observed in these experiments are a specific 

 reaction to gonad secretions or whether they might not be pro- 

 duced in response to secretions from other organs. This point 

 has been subjected to extensive experimental tests with the 

 following results. 



Pieces of organs other than gonads were grafted on chick 

 embryos in the same manner as in the case of gonads. The 

 organs used were: thymus, thyroid, spleen, liver, kidney, and 

 some others. Expeiiments of a similar kind have also been 

 performed in this laboratory by Mr. B. H. Willier, and I had the 



