Urinogenital System 



477 



In bird embryos, hormones introduced into 

 the egg produce typical reversal effects on 

 the gonads (see Wolff and Ginglinger, '35; 

 Willier, Gallagher, and Koch, '35, '37). Fe- 

 male hormone transforms embryonic testes 

 into ovotestes or ovaries, by reduction of the 

 medullary zone and differentiation of cortex 

 (Fig. 183). Male hormones transform ovaries 

 by repression of the cortex with raedullary 

 hypertrophy. The relative value of constitu- 

 tional vs. hormonal factors is illustrated 

 clearly in consequence of the interesting 



have not been regarded as significant. An ex- 

 ception has recently been found in the effects 

 of estrogen on the testes of new-born opossum 

 embryos (Burns, '50). Extensive persistence 

 of the germinal epithelium was found, and 

 in a few cases typical ovotestes were obtained, 

 except that the induced cortex was sterile 

 (Fig. 184). Histological changes followed 

 the usual sequence: repression of testicular 

 development, followed by reactivation of the 

 germinal epithelium to produce a cortex. 

 This result suggests that transformation of 



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Fig. 183. Ovotestis developed from the left gonad of a genetic male chick by treatment with female hor- 

 mone. The testicular part of the gonad occupies a central or hilar position; the highly developed cortex is 

 peripheral. (From Willier, '39.) 



lateral differences in organization in birds. 

 The left testis (with its incipient cortical 

 element) reacts at much lower dosages than 

 the right, and with increasing doses is more 

 completely transformed (see Willier, '39). 



Notwithstanding the fact that the gonads 

 of freemartins are often greatly modified 

 (Willier, '21), exposure of mammalian em- 

 bryos to relatively large doses of hormones* 

 has usually had but slight effect on the 

 gonads, although accessory genital struc- 

 tures may be completely transformed. In 

 some cases male hormones produce a limited 

 hypertrophy of the medullary cords of the 

 ovary (lost, '47a; Wells and Van Wagenen, 

 '54) ; and persistense of localized areas of ger- 

 minal epithelium on the testis has been re- 

 ported after the use of either type of hormone 

 (e.g., Raynaud, '42; lost, '47a). Such changes 



* Administered to the mother during pregnancy 

 or, in the case of marsupial embryos, directly to the 

 pouch young. 



mammalian gonads may prove feasible if 

 proper experimental conditions can be real- 

 ized. There is substantial evidence that the 

 gonads are potentially bisexual. In addition 

 to the freemartin, the reversals described in 

 rat gonads (p. 474) must be noted, and the 

 anomalous occurrence of hermaphroditis- 

 mus verus, characterized by well differen- 

 tiated ovotestes, is well known in many mam- 

 mals. 



DIFFERENTIATION OF THE ACCESSORY 

 GENITAL STRUCTURES 



On the basis of embryological origin the 

 accessory genital structures of vertebrates 

 comprise three main groups: (1) the sex 

 ducts and associated structures, of nephric 

 origin; (2) derivatives of the cloaca or the 

 urinogenital sinvis; and (3) copulatory struc- 

 tures, which develop from the genital tuber- 

 cle. For a detailed account of the origin and 



