70 FRANK R. LILLIE. 



presumable from its testis, at a period very closely approximated 

 to the beginning of visible sex differentiation, which has a specific 

 inhibitory action on proliferation of the germinal epithelium and 

 on the rate of growth of the ovary as a whole. 



This case is an isolated one so far as the early stage is con- 

 cerned. There are, therefore, certain restrictions in generalizing 

 from it. The other evidence that we have demonstrates, however, 

 that the general relations in this case are typical. But it is prob- 

 able that actual vascular connection between the two embryos may, 

 in some cases, be established earlier, and, in other cases, somewhat 

 later. We considered in section 4 the idea that the quantitative 

 aspect of the vascular interchange is probably not an important 

 factor in the degree of intersexuality of the free-martin ; that we 

 are dealing, in other words, with a reaction of the " all-or-none " 

 type. So far as we can see, then, the principal factor, so far as 

 hormones are concerned, in determining the range of variation 

 within the free-martin series is probably the time, in relation to 

 the early stages of sex differentiation, at which vascular inter- 

 change is established. But to supplement this, I believe it is neces- 

 sary to assume that different individuals vary in the state of bal- 

 ance of the zygotic sex factors, and this may influence the quanti- 

 tative effect of the hormone factor. 



It is probable from these results that the ovary does not produce 

 a sex hormone at such early stages. If it were doing so, some 

 reciprocal effect upon the male ought to be observed in some cases 

 at least. The histological evidence is just as negative as the physi- 

 ological in the case of the ovary, while in the case of the testis 

 fully differentiated interstitial cells are found from the 3 cm. stage 

 of the embryo on (Lillie and Bascom, '22). Mr. Bascom will deal 

 with this subject in detail in his study, but I may here call attention 

 to the fact that all students of ovarian hormones locate the cells of 

 origin in the cortex of the ovary, and that this part of the ovary 

 is in its earliest state of origin in the stages in question, and ex- 

 hibits as yet no differentiation of cells of internal secretion. 



Moore (1921) and Sand (1919) have denied Steinach's idea 

 of a mutual antagonism of testis and ovary of mammals by show- 

 ing that the coexistence of both gonads in the same body is possi- 

 ble. The present results show, however, that prior to the forma- 



