478 



Special Vertebrate Organogenesis 



early development of these structures see 

 Wiliier ('39). 



The differentiation of the accessory sex 

 structvires has been studied experimentally in 

 various ways. As in the case of the gonads, 

 different forms of grafting were first em- 

 ployed. Eventually grafting was largely 



throughout life in the males of many species 

 as complete if somewhat rudimentary struc- 

 tvires. An ideal basis for sex reversal is thvis 

 provided. In male urodeles elaborate cloacal 

 glands develop, which in females are absent, 

 rudimentary, or (in some species) differently 

 specialized. The dimorphism of these struc- 



«t :•; ' ;- V ' •'. ' *♦ • "<J >$.-^>- 'iy^'^^. 





Fig. 184. Stages in the development of oxotestes in opossum embryos after treatment from birth with 

 female hormone. A. Persistence of a thick germinal epithelium on a greatly retarded testis of 14 days 

 (X 500). B, Ovotestis of a male aged 30 days (X 150), in which the medullary zone is separated from a 

 sterile cortex by a thick, fibrous tunica albuginea. (From Burns, '50.) 



superseded by administration of pure hor- 

 mones. The development in recent years of 

 methods of castrating embryos has provided 

 crucial evidence, and tests of the self- 

 differentiating capacities of sex primordia 

 in physiological isolation have lately been 

 utilized. 



Results of Grafting Methods. Grafting tech- 

 niques have been mainly confined to amphib- 

 ians and birds. The structures to be con- 

 sidered in amphibians are the sex ducts and 

 the glands of the cloaca. In many amphibians 

 both gonaducts are retained indefinitely; 

 the Wolffian ducts function as excretory ducts 

 in both sexes, and Miillerian ducts persist 



tures is controlled by the gonads. After cas- 

 tration in larval life both ducts remain in a 

 sexually indifferent condition, and cloacal 

 differentiation does not occur (de Beaumont, 

 '33). Gonads grafted into castrates induce 

 differentiation of the appropriate sex duct, 

 and testis grafts cause development of the 

 cloacal glands. When the gonads are trans- 

 formed experimentally (p. 476) the sub- 

 sequent differentiation of gonaducts and 

 cloaca conforms (see Humphrey, '42). 



In bird embryos grafting methods long 

 gave negative results, and the role of hor- 

 mones in sex differentiation was in doubt 

 (see p. 476). It now appears that these fail- 



