120 



BIOLOGIC BASIS OF SEX 



been reported (Raynaud, 1942; Greene, 

 1942). It should be noted that the latter 

 observations are in mammalian embryos 

 (mice and rats) in which the hormone of the 

 testis (see below) is essential to insure re- 

 tention of the ducts. Partial involution in 

 males under the influence of a female hor- 

 mone is possibly only a result of inter- 

 ference with the normal activity of the tes- 

 tis. On the other hand, a paradoxical action 

 of female hormone, causing partial retention 

 and hypertrophy of the male duct, has been 

 occasionally reported (e.g., Greene, 1942; 

 Moore, 1941). Although the method of ad- 

 ministration in these cases does not permit 

 accurate estimation of the dosage it was 

 evidently rather large. With these excep- 

 tions, the effects of sex hormones on the 

 male duct system are consistent with theory. 

 The effects of castration on the develop- 

 ment of the male sex duct are striking and 

 agree with the results of hormone adminis- 

 tration. They show that in all species the 

 presence of the embryonic testis is necessary 

 to induce sexual differentiation of the duct, 

 and to insure its retention in mammalian 

 embryos. In amphibian larvae (Triturus, 

 syn. Triton) the Wolffian ducts persist after 

 castration in their capacity as nephric ducts, 

 but remain in a sexually undifferentiated 

 condition (de Beaumont, 1933). In bird 

 embryos also there is no significant altera- 

 tion of the Wolffian ducts after castration. 

 It is in mammals that the ducts become de- 

 pendent on the testis and its hormone for 

 survival as well as for sexual differentiation. 

 In rabbit embryos castrated before the 22nd 

 day of gestation (Jost, 1947b) the ducts 

 in both sexes completely regress, following 

 the female pattern of development (Fig. 

 2.26) ; involution in castrates is prevented, 

 however, and normal development is main- 

 tained by prompt administration of male 

 hormone. A more variable atresia of the 

 ducts also occurs in fetal rats after castra- 

 tion (Wells and Fralick, 1951). In mice 

 Raynaud reports a difference in reaction in 

 the two sexes. After castration the Wolffian 

 ducts of males undergo a complete involu- 

 tion but they may be partially retained in 

 females. It is suggested that in this species 

 the ovaries may play a positive role in the 

 involution of the duct in females (Raynaud, 

 1950). 



The development of the Woffian ducts in 

 vitro. Further evidence that retention and 

 sexual differentiation of the Wolffian ducts 

 and associated structures (epididymal tu- 

 bules and seminal vesicles) are dependent 

 on the testis and its hormone is provided by 

 the behavior of the male duct system after 

 isolation, using the technique of organ cul- 

 ture. Development in isolation provides a 

 parallel to development in the castrate fe- 

 tus, with exclusion, however, of possible in- 

 fluence by hormones of maternal or pla- 

 cental origin or from some extragonadal 

 source in the fetus. 



When the mesonephric bodies of rat em- 

 bryos, including long segments of the gona- 

 ducts, are removed at 15 to 16 days of gesta- 

 tion and cultured without the gonads, the 

 Wolffian ducts of both males and females 

 degenerate, but at the same time the Miille- 

 rian ducts survive and develop normally. 

 The degeneration of the Wolffian ducts can- 

 not, therefore, be due to unfavorable condi- 

 tions in the medium (Jost and Bergerard, 

 1949) . The same result was obtained using 

 slightly older fetuses of ±16.5 days (Jost 

 and Bozic, 1951). However, the most com- 

 plete study of this question is that of Price 

 and Pannabecker (Price, 1956; Price and 

 Pannabecker, 1956) who explanted male 

 genital tracts of 17.5-day rat fetuses under 

 various conditions designed to test the role 

 of the embryonic testis and the male hor- 

 mone. When both testes are included with 

 the explant, development of the male duct 

 system proceeds normally up to an age of 

 21.5 days (approaching term for the normal 

 fetus I and the seminal vesicles develop as 

 usual. Normal development ensues also 

 when only one testis is left with the implant. 

 But if one testis is removed and the lateral 

 halves of the genital tract are spread widely 

 apart on the surface of the medium, de- 

 velopment is normal only on the side where 

 the testis is present ; on the other side serious 

 defects appear; the duct is thin and weakly 

 developed, and the seminal vesicles are 

 small or even lacking. Finally, if both testes 

 are removed the Wolffian ducts regress com- 

 pletely. However, the addition of male hor- 

 mone to such a prci^aration fully compen- 

 sates for the al)scncc of the testes and 

 development of the male duct system is 

 again normal. 



