ACTION OF SEX HORMONES IN FOETAL LIFE 419 



seen in lateral variations, as for instance in figure 28 where a 

 large gonad on one side is associated wdth a large Wolffian duct, 

 and seminal vesicle, and a much smaller one on the other side 

 mth a correspondingly smaller duct and vesicle. 



When, therefore, we attribute the free-martin condition to 

 the male hormones we only mean to assert that they are the 

 primary cause, and not that they are the decisive factors in each 

 member of the series of events. 



It follows from this discussion that sex in mammals cannot 

 be diagnosed by the character of the gonads alone because a 

 testis-bearing indi\'idual may develop from a female zygote. 

 The unexpected result is reached that the external genitalia and 

 the mammary gland are more reliable criteria of the female sex 

 than the internal parts. 



We have no comparable data on the male side, and we can 

 only speculate as to the transformation that would be produced 

 in the male reproductive system by the action of female hormones 

 beginning before sexual differentiation. Theoretically we would 

 have to assume that the male zygote contains female as well as 

 male factors, but the male zygote may not be capable of such 

 extensive transformation as the female, owing to the embryologi- 

 cal fact that the male gonad never forms normally any homologue 

 of the cords of Pflliger in the female, i.e. of the ovarian cortex, 

 whereas the female does form the homologue of the seminiferous 

 tubules before the cords of Pfliiger begin to arise. In the case 

 of the free-martin we do not find that male hormones cause 

 the development of any structure which is not represented 

 embryologically in the normal female; the hormones act in this 

 case merely by inhibition or stimulation of normal embryonic 

 rudiments. If this should hold as a principle also on the male 

 side we could not expect that the transformation of a testis into 

 an ovary should ever occur, although suppression of complete 

 testicular development would probably happen. But apart from 

 this admittedly uncertain principle there is no reason for assuming 

 that the possibility of the male zygote for acquisition of female 

 characters may be any less than the reverse case. 



For their proper evaluation the results concerning the free- 

 martin should be associated with the other studies indicating that 



