Urinogenital System 



481 



or seventh day; later treatment has no effect 

 (Stoll, '48; cf. the stabilizing effect of female 

 hormone on male Miillerian ducts). Again 

 there is a critical period after which suscep- 

 tibility is lost. 



In larval amphibians the Miillerian ducts 

 develop slowly. Treatment with male hor- 

 mone during the backward growth of the 

 duct suppresses the unformed portion, but 



ferentiation of the glands in larvae of either 

 sex (see Burns, '39; Mintz, '47) and a male 

 type of cloaca. 



The urinogenital sinus of mammals is de- 

 rived embryologically from the cloaca. In 

 its primitive condition it receives the sex 

 ducts near the neck of the bladder, and opens 

 externally at the base of the genital tubercle. 

 Differentiation in females is characterized by 



-O^-:.. 





Fig. 187. Development of the sinus region and prostate in young opossums aged 50 days, after treatment 

 from birth with male hormone (from Burns, '49). A, Section of normal male sinus showing prostatic glands; 

 B, male receiving hormone, showing enormous hypertrophy of the prostate; C, female showing great de- 

 velopment of the prostate induced by male hormone; D, normal female, characterized by vaginal canals and 

 complete absence of prostatic glands; V, terminus of vaginal canal. 



the part already present persists, and with 

 large doses paradoxically hypertrophies (see 

 Mintz, '47). In mammalian embryos com- 

 plete suppression of the Miillerian ducts is 

 not obtained, but the vaginal region may 

 be inhibited, e.g., in opossums (Biu'ns, '42) 

 and in mice (Raynaud, '42). On the contrary, 

 paradoxical stimulation occurs readily (e.g., 

 Moore, '47; Burns, '49), but is not found 

 with low dosages (Burns, '42, '45a). 



Reactions of Cloaca and Urinogenital Sinus 

 to Hormones. The development of cloacal 

 glands in amphibians is conditioned by male 

 hormone; the response of the cloaca to castra- 

 tion and to testis grafts has been noted (p. 

 478). Male hormones induce precocious dif- 



formation of the vagina, while the male 

 ducts retrogress. In the male, regression of 

 the Miillerian ducts and development of the 

 complex of prostatic glands are the chief 

 features (Fig. 186). Male hormones produce 

 a male type of sinus in both sexes (for de- 

 tails see Greene, '42; Raynaud, '42, '50; 

 Moore, '47; Burns, '49; Jost, '50; Wells and 

 van Wagenen, '54). The differentiation of 

 males is accelerated; females imdergo trans- 

 formation — vaginal development is partly or 

 entirely suppressed and prostatic glands de- 

 velop (Fig. 187). Conversely, female hor- 

 mone suppresses prostatic differentiation and 

 produces a sinus of female form, with a vagi- 

 nal type of epithelium. Permanent suppres- 



