Urinogenital System 



479 



ures were due merely to a quantitative in- 

 sufficiency of hormone, since gonads grafted 

 directly into the embryo are effective. Grafted 

 ovaries induce partial retention of Miillerian 

 ducts in male embryos, while testes stimulate 

 Wolffian ducts and completely inhibit Miil- 

 lerian ducts in both sexes (Wolff, '46). Sim- 

 ilar results have recently been obtained by 

 multiple testis grafts on the chorio-allantois 

 (Huijbers, '51). 



consult Colloques Internationaux, Centre Na- 

 tional de la Recherche Scientifique (Paris, 

 1951); La Differenciation Sexuelle chez les 

 Vertebres. ] 



It is not possible to consider all findings in 

 detail, but as a basis for discussion the prin- 

 cipal results may be summarized as follows: 



1. Sex hormones have sex-specific effects on 

 the development of genital structures, either 

 by direct action on the individual primordia. 



Fig. 185. Development of the sex ducts in chick embryos after treatment with sex hormones (from Willier, 

 '39). A, Normal female embryo incubated 18 days; B, male embryo treated with female hormone — both 

 oviducts are present and greatly hypertrophied; C, normal male embryo of 17 days showing complete ab- 

 sence of oviducts; D, female embryo treated with male hormone — -the oviducts are absent except for small 

 fragments anteriorly, and the Wolffian ducts are greatly hypertrophied. 



Gonad grafting has only recently been 

 utilized in mammalian embryos, chiefly with 

 a view of counteracting the effects of castra- 

 tion. The results are positive, and will be 

 mentioned in that connection. 



Administration of Hormones. The production 

 of steroid hormones in pure form enor- 

 mously accelerated the experimental study of 

 sex differentiation. For the first time it 

 became possible to attack the problem in 

 mammals by administration of effective 

 doses during pregnancy. The different experi- 

 mental conditions under which hormones 

 have been used, in many different groups 

 and species, have inevitably led to variable 

 and sometimes inconsistent results. [For re- 

 views and analyses of a large literature see 

 Wolff ('38, '47); Willier ('39); Humphrey 

 ('42); Raynaud ('42); Mintz ('47); Moore 

 ('47); Price ('47); Jost ('48); Ponse ('49); 

 Burns ('49). For a recent synopsis of the field 



or by acting indirectly, as in release from 

 inhibition, or via other endocrine agencies. 



2. In general, male hormones accelerate 

 differentiation of male structures and inhibit 

 certain female structures, in embryos of both 

 sexes; they also induce certain male pri- 

 mordia in females. Conversely, female hor- 

 mones stimulate the development of female 

 structures and inhibit certain male pri- 

 mordia. 



3. In addition to their usual effects, how- 

 ever, both types of hormone in many cases 

 paradoxically stimulate structures of the 

 other sex. 



If the effects of hormones as outlined above 

 are in general consistent with theory, the 

 occurrence of so-called "paradoxical effects" 

 is discordant, and has been differently inter- 

 preted. It is denied by some that the effects 

 of steroid hormones are in any sense spe- 

 cific, and the validity of the hormone theory 



