114 BENJAMIN H. WILLIER 



the gonads may be intersexual. The rather frequent occurrence 

 of intersexual gonads in the pig may have some such explanation 

 as this. The appearance of intersexual gonads in mammals, 

 which, as a rule, furnish no possibilities of the intermingling of 

 sex hormones through the fusion of foetal membranes, must be 

 interpreted in some other way. In such cases it is not impossi- 

 ble that disturbances in the normal relationship of the maternal 

 blood supply to the foetal blood may account for the intersexual 

 condition of the gonads. 



The definite transformation of an ovary into a testis raises 

 the question of the existing morphological homologies between 

 the two reproductive glands. As early as 1870, Waldeyer, in 

 his classic book, ''Eierstock und Ei, " suggested that the poten- 

 tialities for the development of both ovary and testis existed in 

 the same individual, but he erred in considering that the male 

 and female reproductive glands arise from different portions of 

 the genital ridge. From a study of the adult gonads of the bat. 

 Van Beneden ('80) formulated the hypothesis that the testis 

 and ovary possess morphological structures in common. He 

 homologized medullary cords with seminiferous tubules, medul- 

 lary tubes with straight tubules, and the rete ovarii with the 

 rete testis. Such a homology as suggested was not fully justified 

 until the comparative studies on the development of the ovary 

 and testis were made by various investigators. Allen ('04) 

 showed for the rabbit and pig that the first set of sexual cords 

 (medullary cords) of the ovary and of the seminiferous tubules 

 of the testis are homologous structures, which are both formed 

 as tubular invaginations of the epithelium of the genital ridge. 

 Simultaneously with the development of the first set of sexual 

 cords, the rete cords of both ovary and testis arise in the same 

 manner from the epithelium of the anterior end of the genital 

 ridge. A zone of connective tissue, the primary tunica albuginea, 

 which lies between the medullary cords and the cords of Pfluger, 

 is homologous with the tunica albuginea of the testis. 



In man (Felix, '11) and in the cat (Kingsbury, '13) the mor- 

 phological homology of the medullary cords of the ovary and 

 the seminiferous tubules of the testis appears difficult to establish 



