144 



BIOLOGIC BASIS OF SEX 



onic ovaries grafted into the coelomic cavity 

 induce cortical differentiation in the testes 

 of male hosts at a very early stage, and dur- 

 ing the same period testis grafts inhibit the 

 difTerentiation of the IMiillerian ducts. A 

 similar effect is observed when histologically 

 undifferentiated gonads of duck embryos 

 are cultured in vitro in close contact (Wolff 

 and Haffen, 1952b). When ovaries and tes- 

 tes are thus associated the latter exhibit 

 typical reversal changes from the very be- 

 ginning of sexual differentiation. 



In mammals the activity of the testis 

 hormone in the early stages of sex differen- 



tiation is revealed by the promptness with 

 which castration effects appear. In the ab- 

 sence of the testes, changes in certain ac- 

 cessory sex structures are evident as soon 

 as sexual differentiation can be observed. 

 In the case of the prostate the hormone is 

 actually necessary for the appearance of 

 the primary buds. Conversely, implantation 

 of an embryonic testis into a female rabbit 

 embryo inhibits the Miillerian ducts and 

 initiates development of male accessory 

 structures (Fig. 2.35; for a more detailed 

 summary see Willier, 1955). 



The source of the hormones produced by 



Ostium of Mullerian Duct 



fted Testl 



Fig. 2.35. Localized effects of an embryonic testis grafted to the broad ligament of a fe- 

 male rabbit embryo (Jost, 1947b). The inhibitory effect of the grafted testis has caused a 

 great reduction in the size of the host ovary and has suppressed the Mullerian duct (un- 

 shaded) in the vicinity of the graft. These structures are normal on the opposite side. Con- 

 versely, the testis has induced complete retention of the Wolffian duct and epididymis 

 (stippled) on the side of the graft and a partial retention on the other side. The influence of 

 the graft is strongest in its immediate vicinity and beyond a certain distance disappears, 

 indicating that the hormone spreads locally by diffusion rather than through the circulation. 

 The results also suggest that the stimulatory action on the male structures is stronger than 

 the inhibitory effect on the Miillerian duct, since it extends further. Such a situation prob- 

 ably results from threshold differences in reactivity of the two end-organs to the testis hor- 

 mone. 



