author's abstract of this paper issued 

 by the bibliographic service, march 14 



STRUCTURES AND HOMOLOGIES OF FREE-MARTIN 



GONADS 



BENJAMIN H. WILLIER 



Hull Zoological Laboratory, University of Chicago 



EIGHTEEN FIGURES 



INTRODUCTION 



A female which is born co-twin with a normal male in cattle is 

 usually sterile, and is known among stockmen as a 'free-martin.' 

 The internal reproductive organs of such a female are decidedly 

 male-like, and the external genitalia are usually female-like, 

 although they may be modified also in the male direction. Lillie 

 ('17) showed that the sterile free-martin is zygotically a female 

 which is modified in the male direction by the action of sex 

 hormones from the male twin. These hormones circulate in the 

 vascular systems of both foetuses, owing to the establishment of 

 a common circulation by an early fusion of the embryonic mem- 

 branes and the anastomosis of the extra-embryonic blood-vessels 

 of the two individuals. If no vascular connections between the 

 twins are made, the female is a 'fertile free-martin.' 



The effect upon the foetal reproductive glands of the introduc- 

 tion of the hormones from the male embryo into the circulation 

 of the female twin was described by Chapin ('17). The repro- 

 ductive organs which are present in the indifferent stage at the 

 time when the secretion from the male enters the circulation of 

 the female develop toward the male condition, while those 

 structures which would develop at the time of sex differentiation 

 in the normal female, are absent. That is to say, the tunica 

 albuginea, first set of sex cords, ^ rete testis, and epididymis 



^ The term sex (or sexual) cord is used to include the invaginations of the ger- 

 minal epithelium, whether they are male or female structures; in the case of 

 the testis there is one set of sexual cords, which are destined to form the func- 



63 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 33, NO. 1 



