HORMONES IX DIFFERENTIATION OF SEX 



101 





Fig. 2.18. A. Testis of an opossum aged 20 days, converted into an ovotestis by the action 

 of estradiol dipropionate. Internally the reduced and disorganized medullary region is seen, 

 separated from the external cortical zone by the well defined, fibrous tunic layer. The large, 

 irregular ca\ity in the upper center, lined by a heavy eiuthelium, is the rete testis. B. De- 

 tail at higher power of the cortex, showing the structure of the cortical cords (which are 

 sterile) and the highly developed germinal epithelium. 



stage 34 if the germinal epithelium is to be 

 preserved. In earlier experiments, in which 

 treatment was begun after stage 35, there 

 were no significant effects on the differen- 

 tiation of the gonads, even in cases where 

 almost complete transformation of the ac- 

 cessory sex structures had occurred. It is 

 now evident that in these experiments the 

 first application of the hormone came too 

 late to prevent involution of the germinal 

 epithelium, thus precluding development of 

 a cortex. Also of importance is the dosage, 

 which must be kept at a low level to secure 

 a good result. This point is crucial for the 

 survival of germ cells in the developing cor- 

 tex. High dosages always result in com- 

 plete sterilitij of the cortical zone, even when 

 this layer is otherwise well developed (Fig. 

 2.18). With lower doses, however, germ cells 

 are found in limited numbers in the cortex, 

 sometimes sparsely scattered, sometimes in 

 small groups, and not infrequently these 

 cells display the cytologic characters of 

 young ovocytes (Fig. 2.20). Often there is 

 a considerable growth of the cytoplasm and 

 well formed primordial follicles are seen 

 (Fig. 2.20B). 



Treatment with relatively low doses of 

 estradiol (of the order of 0.2 to 0.3 fxg. per 

 day) from birth to an age of 20 days pro- 

 duces a remarkable transformation of the 

 testis, which retains hardly any normal fea- 

 tures (Burns, 1956b). Rather, it presents 

 the appearance of a somewhat atypical 

 ovary (Fig. 2.19B). The only remnant of 

 testicular structure is a small, central nodule 

 at the junction of the rete canals, and the 

 massive cortical zone is covered externally 

 by a thick germinal epithelium. The cortex 

 of the transformed testis contains germ cells 

 in considerable numbers, including a few 

 large ovocytes. Views of cortical areas in 

 gonads of this group are shown in Figure 

 2.20.4 and B. In more recent experiments, 

 using still lower doses and a longer period 

 of treatment (thus far the longest experi- 

 ment has extended to an age of 33 days post- 

 partum ) , the result is even more striking, 

 the structure of the cortex in many cases ap- 

 proximating that of normal ovaries. Always, 

 however, certain remnants of testicular 

 structure ]icrsist in the medullary region 

 (Fig. 2.21, compare A and B). The number 

 of ovocytes in the cortex is enormously 



