Urinogenital System 



483 



Miillerian dvicts differentiate autonomously. 

 It should be recalled in this connection that 

 the regression of the Miillerian ducts in 

 male embryos is prevented by female hor- 

 mone (p. 480). Their retention in such case 

 might be due initially to inhibition of the 

 testes, but when there is also marked hyper- 

 trophy of the ducts a direct stimulation must 

 be involved. 



The effects of castration on the male sex 

 ducts vary in different forms (Fig. 189). In 

 larval amphibians and in chick embryos the 

 Wolffian ducts, which serve as nephric ducts, 

 remain after castration in a sexually undif- 

 ferentiated condition (de Beaumont, '33; 



tance of the time factor. Castration on the 

 twenty-third or twenty-fourth day is fol- 

 lowed by almost normal development; if per- 

 formed somewhat earlier the prostatic buds 

 are arrested and differentiate no further. 

 Castration before the twentieth day sup- 

 presses all development — the buds do not 

 appear. The effects of castration are entirely 

 prevented by male hormone or by grafts of 

 the embryonic testis (Jost, '50; Wells, '50). 

 The copulatory structures are also highly 

 sensitive to castration. Castrated mammalian 

 embryos of both sexes develop external geni- 

 talia of female type (see Jost, '47b, '50; 

 Raynaud and Frilley, '47; Raynaud, '50), but 



BIRDS 



Fig. 189. Table summarizing the effects of castration in embryos of birds and mammals, based on the 

 reports of Wolff ('50) and Wolff and Wolff ('51) in the chick and duck; Huijbers ('51) in the chick; Jost 

 ('47b, '50) in the rabbit; Raynaud and Frilley ('47) and Raynaud ('50) in the mouse. Similar but less severe 

 effects have been obtained in the rat (Wells, '50; Wells and Fralick, '51); but Moore ('47) reports little 

 effect in young opossums castrated at the age of 22 days. The asterisk indicates that partial persistence of 

 Wolffian ducts may occur in castrate female mice (see Raynaud, '50). 



Wolff, '50). In mammals their retention and 

 sexual differentiation in the male appear to 

 depend upon the testis; they regress in cas- 

 trate rabbit fetuses, as in the normal female 

 (Jost, 47b, '50). [There is an indication in 

 mice that the Wolffian ducts may persist in 

 part in castrate females, suggesting that the 

 ovary may have a role in the regression of 

 the ducts in normal females (see Raynaud, 

 '50).] 



Castration prevents development of the 

 male urinogenital sinus and accessory glands, 

 but female castrates are virtually normal 

 (Fig. 189). In males, development of the 

 vagina (in conjunction with retention of the 

 Miillerian ducts) gives the sinus a female 

 form. Prostatic differentiation is suppressed 

 (Jost, '47b), and in mice coagulating glands 

 are also absent (Raynaud, '50). The effects 

 in the rat embryo are less severe, depending 

 perhaps on time of operation (Wells and 

 Fralick, '51). With respect to the prostate, 

 the results in the rabbit are especially clear 

 (Jost, '47c), illustrating the great impor- 



the effects of castration are prevented by 

 male hormones. As in the case of the duct 

 systems and the sinus structures, normal 

 male development evidently depends on the 

 testis, while the female pattern develops 

 without hormonal conditioning, in a so- 

 matic or asexual manner. In bird embryos, 

 however, the situation is reversed, the male 

 sex representing the asexual type (Wolff 

 and Wolff, '51). 



SOME SPECIAL PROBLEMS AND 

 CONSIDERATIONS 



Patterns of Hormonal Control. The hormone 

 theory of sex differentiation was developed 

 by Lillie and his associates with special ref- 

 erence to the case of the freemartin. The 

 dominance of the male twin was explained 

 on the grounds that the testis produces its 

 hormone before the ovary; in fact, no sug- 

 gestion of endocrine activity in the ovary 

 was seen until late in fetal life. The domi- 

 nant role of the male hormone was thus 



