EFFECTS OF GONAD GRAFTS IN CHICKS 39 



SUMMARY 



1. The purpose of this investigation was to determine whether 

 or not sexual differentiation is controllable and reversible through 

 the action of sex-hormones. 



2. The common fowl was used as material. 



3. A small piece of testis or ovary was grafted on the chorio- 

 allantoic membrane of a developing chick. Testes and ovaries 

 used for grafting were taken from birds varying in age from an 

 eight-day-old embryo to the adult. The embryos upon which 

 the grafts were implanted varied in age from two to sixteen 

 days at the time of the operation. 



4. In a number of cases the grafts grew and established vascu- 

 lar connections with the allantoic blood-vessels. 



5. A certain number of the embryos upon which the gonad 

 grafts had proved successful exhibited a greater or less degree 

 of modification of their reproductive systems. The most impor- 

 tant alterations were these : 



a. The simultaneous existence of gonads of the male type and 

 differentiated miillerian ducts of the female type. 



h. An alteration of the normal size ratio of the two testes. 

 Whereas the two testes in the normal male are of the same size 

 at hatching, in many of these cases the left testis was markedly 

 larger than the right one. 



c. Persistence of the right gonad in female-type embryos. 

 The right gonad disappears in normal female embryos. 



6. In normal chicks it was found that the wolffian ducts are 

 persistent in the female. 



7. Grafts of liver, spleen, thyroid, thymus, and other organs 

 on chick embryos produce absolutely no modifications of the 

 reproductive system. 



8. The- results demonstrate that the testis and ovary produce 

 secretions which have definite and specific physiological func- 

 tions and which are capable of modifying the primary sexual 

 characters. 



9. It is shown by these experiments that sexual differentiation 

 may be reversed in the chick. This result supports the expla- 

 nation advanced by Lillie to account for the production of the 

 free-martin in cattle. 



