HORMONES IX DIFFERENTIATION OF SEX 



99 



the degree of intersexiiality and the number 

 of intersexual gonads steadily increase 

 (Wolff, Strudel and Wolff, 1948). Since 

 various accessory sex structures also show 

 paradoxical reactions the problem will ap- 

 pear again. 



3. Effects of Grafting Gonads into the Coe- 

 lomic Cavity 



The demonstration that steroid sex hor- 

 mones are capable of inducing sex trans- 

 formation in avian gonads led to a reinvesti- 

 gation of earlier failures to obtain reversal 

 by means of chorioallantoic grafting. Even- 

 tually it was shown that the difficulty was 

 largely a matter of the method. When gonad 

 primordia are transplanted directly into the 

 coelomic cavity of a host embryo of different 

 sex, varying degrees of transformation, or 

 even a virtual reversal, are obtained. 



The first experiments of this type were 

 only a partial success (Bradley, 1941). Em- 

 bryonic gonads of the chick and the duck, 

 isolated at 96 to 120 hours of incubation, 

 were inserted into the body cavity of host 

 embryos through a small slit in the somato- 

 pleure, using both homoplastic and hetero- 

 plastic host-graft coml)inations. In the case 

 of the chick, host embryos were always con- 

 siderably younger than donors. In all cases 

 the grafts underwent primary sex differenti- 

 ation in accordance with genotype, and only 

 a small minority showed specific modifica- 

 tions. The results were rather inconclusive 

 because in no case were the changes of a 

 conspicuous character, and there was great 

 variability in the growth and differentiation 

 of the grafts, making it difficult to assess 

 the significance of the modifications. In 

 some cases changes of the same type ap- 

 peared in the gonads of the host embryo. 



The modifications noted by Bradley fall 

 into three main classes. (1) Vacuolation of 

 the medullary cords of testes growing in fe- 

 male hosts (in a few cases) caused them to 

 resemble the hollow medullary cords of 

 ovaries. (2) In some cases ovaries growing 

 in male hosts developed solid medullary 

 cords of male type. (3) Rudimentary right 

 ovaries (always testis-like in character) had 

 a tendency to become enlarged when grow- 

 ing in male hosts. A similar effect was some- 

 times seen in the right ovaries of hosts bear- 



ing testis grafts. No ready explanation was 

 available for the inconstant occurrence of 

 these effects or for their quantitative varia- 

 bility, because no clear correlation was 

 found between the degree of modification 

 and the relative proximity of the interacting 

 gonads. Finally, similar changes appeared in 

 a few cases when the host-graft combina- 

 tions involved the same sex; consequently 

 the specific character of the modifications 

 was left in doubt. 



The matter was clarified by the experi- 

 ments of Wolff (1946) who used a modifica- 

 tion of the method with better results. Grafts 

 taken from older embryos (6 to 11 days) 

 were implanted into hosts of about 50 hours 

 of incubation. Under these conditions a 

 striking transformation of gonad differentia- 

 tion was obtained in the host, and in addi- 

 tion the developing gonaducts [q.v.) were 

 strongly modified. Ovaries grafted into male 

 hosts induced differentiation of cortex on 

 the left testis to such an extent that it some- 

 times approached the structure of an ovary. 

 The right testis (which was usually more 

 distant from the graft) was less modified 

 but its growth was inhibited. On the con- 

 trary, implantation of a testis in the same 

 manner produced no important effect on the 

 differentiation of the ovaries of the host but 

 the development of the Miillerian duct was 

 strongly inhibited indicating that the graft 

 is endocrinologically active. In their histo- 

 logic character the effects of gonad grafts 

 are similar to those produced by crystalline 

 hormones, differing only, as a rule, in being 

 more localized in relation to the position of 

 the graft. The demonstration in this experi- 

 ment that, physiologically, the ovary is the 

 dominant gonad in birds is consistent with 

 the earlier observation that relatively larger 

 doses of pure hormones are required for the 

 transformation of ovaries than for testes. 



These positive results after so many fail- 

 ures suggested that the ineffectiveness of 

 chorioallantoic grafts in the earlier experi- 

 ments was possibly a matter of hormone 

 production, failure of the graft to maintain 

 a sufficient level of the hormone in the blood. 

 This view is substantiated by the later ex- 

 periments of Huijbers (1951) who showed 

 that multiple grafts of well differentiated 

 testes on the chorioallantois have marked 



