ACTION OF SEX HORMONES IN FOETAL LIFE 397 



therefore, in all probability a case in which the circulations of 

 the three indi\dduals anastomosed, and in which the male 

 sterilized both females. 



IV. THE HORMONE THEORY OF THE FREE-MARTIN 



We may now proceed to a consideration of the argmnent for the 

 hormone theory. In our previous considerations we have dwelt 

 upon the separate zygotic origin of the free-martin, and the foetal 

 vascular connections; it is obvious that these conditions suggest 

 a hormone theory; but, before such a theory could be regarded 

 as demonstrated an explanation of the existence of fertile free- 

 martins would need to be offered, and the limitation of the phe- 

 nomenon of sterility of the free-martin to cattle as a common 

 occurrence would have to be explained; the possibility of the 

 existence of sex hormones at such an early period of the foetal 

 life would also need to be demonstrated, and reason for limitation 

 of the sterilizing effect to the female is needed. 



We shall consider first the fertile free-martin; three cases of a 

 normal female twin to a male have been found in my 24 cases of 

 bovine two-sexed foetal twins. These are readily explained 

 a -priori on the hormone hypothesis on the supposition that they 

 represent cases in which anastomosis of the foetal blood-vessels 

 did not occur. It is important to notice that such cases are ex- 

 ceedingly crucial, for if we should find a case of two-sexed bovine 

 twins in which foetal vascular anastomosis was absent, and in 

 which the female was nevertheless a sterile free-martin, the 

 hormone theory would have to be abandoned. 



The first two cases of fertile free-martins were nos. 8 and 9 of 

 my series (figs. 7 and 8) ; they were collected before the hormone 

 theory was formed and the records are incomplete. In my note- 

 book I had merely recorded that the connection between the two 

 chorions of each pair was narrow; it was probably not vascular, 

 but this cannot be certainly known, and these cases must be 

 left out of consideration. Fortunately the third case, no 40, is a 

 veritable experimentum crucis. In this case organic connection 

 of the two chorions was entirely lacking. The central ends of the 

 two chorions merely overlapped in the body of the uterus, and fell 



