HORMONES IN DIFFERENTIATION OF SEX 



97 



Fig. 2.13. Histologic difYerentiation in the gonads of duck embryos developing in vitro, 

 after isolation just at the beginning of sexual differentiation (Wolff and Haffen, 1952a). A. 

 Normal form and histologic differentiation of the testis in comparison with an ovary develop- 

 ing under the same conditions (B). C and D show, respectively, the structure of these gonads 

 under higher magnification. (From Et. Wolff and K. Haffen, J. Exper. Zool., 119, 381-404, 

 1952.) 



lagher and Koch (1935, 1937) ; and Dant- 

 chakoff (1935, 1936) who introduced steroid 

 hormones into incubating eggs before the 

 beginning of sex differentiation. The results 

 vary in detail but are consistent in the main 

 outlines; they may be stated briefly, follow- 

 ing chiefly the reports of Willier, Gallagher 

 and Koch and of Wolff and Ginglinger. 



Female hormones (estrone or estriol) do 

 not significantly affect the differentiation of 

 embryonic ovaries but testes are highly 

 transformed. Because of the better develop- 

 ment and longer survival of the germinal 

 epithelium the left testis is more amenable 

 to reversal than the right. Relatively low 

 doses convert it into an ovotestis. The distal 

 ends of the medullary cords become hol- 

 lowed out into tubular structures like the 

 medullary cords of the ovary (Fig. 2.14.4) ; 

 at the same time a zone of cortex develops 

 peripherally, arising as a proliferation of the 

 germinal epithelium. A small, unchanged 

 medullary mass usually persists at the hilus. 

 But with larger doses even this may dis- 

 appear and the cortex becomes much thicker. 



Such cases are practically indistinguishable 

 from ovaries. The right testis, however, is 

 more difficult to transform. In the above ex- 

 periments it was not greatly modified at 

 lower dosages ; even when the left testis was 

 almost completely transformed into an 

 ovary the right never entirely lost its tes- 

 ticular character. Because of the poor de- 

 velopment of the germinal epithelium its 

 capacity to produce cortex is limited. How- 

 ever, Wolff (1948) made a special study of 

 the right gonad in both sexes, assuming that 

 stimulation of the gonad at an earlier stage, 

 before regression of the germinal epithelium 

 can be detected in either sex, might reveal 

 a greater capacity for cortical differentia- 

 tion. To insure rapid action a water soluble 

 form of the hormone was used. In this way 

 a considerable differentiation of cortex was 

 obtained. The importance of a persistent 

 search for the proper experimental condi- 

 tions is again demonstrated. 



Male hormones, on the other hand, are 

 less effective in transforming the embryonic 

 ovaries of birds. Again lateral differences in 



