404 FRANK R. LILLIE 



These data relate for the most part to the pig, but there is no 

 doubt that we are justified in assuming that the processes in 

 cattle would not differ essentially; and hence that at the time of 

 sex-differentiation in cattle there is an active secretion of male 

 sex hormones which pass into the blood, and thus in the case of 

 twins by the vascular anastomosis reach the circulation of the 

 other twin. At this time, if the other twin is a female, the cords 

 of Pfliiger have hardly begun to form; no interstitial cells can 

 therefore be present ; hence there can be no conflict of hormones. 

 Now Miss Chapin's study of the embryonic gonad of the sterile 

 free-martin shows that the cortex of the ovary does not develop 

 in these animals. Hence no conflict of sex hormones arises; 

 hence also, there can be no question of the male of two-sexed 

 twins being influenced in its sexual development by its mate. 



There is at least no escape from the conclusion that it is the 

 circulation of the blood of the male twin in the female that ac- 

 counts for the results. The probability of the presence of inter- 

 stitial secretion of the testis in the blood of the male at the time 

 of beginning sex differentiation and the limitation of the action 

 of the male blood to the reproductive system of the female are the 

 reasons for attributing the effect to sex hormones of the male. 

 The possibility of course exists that the blood of the male in such 

 foetal stages differs from that of the female in this specific re- 

 spect owing to other causes than secretion of interstitial cells of 

 the testis; but there seems to be no reason for making such an 

 assumption . 



In my preliminary paper I left open the question whether the 

 invariable result of sterilization of the female at the expense of 

 the male was due to more precocious development of the male 

 hormones, or to a certain natural dominance of male over female 

 hormones. It now appears from the results of more detailed 

 investigation that the latter alternative probably does not arise. 



The main assumptions that are involved up to the present 

 point are (1) that cattle resemble pigs with reference to the early 

 origin of interstitial tissue in the testis; (2) that such tissue has in 

 foetal life properties similar to those that have been demon- 

 strated in post foetal life by a considerable number of investi- 



