96 



BIOLOGIC BASIS OF SEX 



INDIFFERENT STAGE 



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RIGHT GONAD LEFT GONAD 



EFFECTS OF ? HORMONE ON MALE 



EFFECTS OFd* HORMONE ON FEMALE 



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Omg \l'^\i\i\i\llll/l/yf\ 

 LEFT TESTIS 



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 RIGHT OVARY LEFT OVARY 



Fig. 2.12. Diagrams sliowing lateral differences in gonad organization in the chick embryo 

 with respect to the representation of cortical and medullary elements; and differences in 

 reaction to sex hormones based on these differences. (After N. T. Spratt, Jr., and B. H. 

 Willier, Tabulae Biologicae, 17, 1-23, 1939). Note the stronger representation of the cortical 

 component in the left gonad in both sexes, and its influence on the responses of gonads to 

 hormones in relation to dosage. For details see text. 



structural differences are correlated with 

 different capacities for sex reversal under 

 experimental conditions, as will appear.^ 



The experimental study of sex differentia- 

 tion in birds has been limited largely to two 

 domestic species, the chick and the duck. 

 Histologic sex differences first appear in the 

 gonads of these species around the seventh 

 and the ninth days of incubation, respec- 

 tively, but the future pattern of develop- 

 ment is essentially determined much earlier. 

 This is shown by the fact that when the 

 sexually indifferent gonads of chicks are 

 transplanted at the genital ridge stage to the 

 choi'ioallantoic membrane of another em- 

 bryo, they continue in most cases to develop 

 independently, in accordance with genotype, 

 giving rise to typical testes or ovaries, and 

 in the case of gonads of female constitution 

 to characteristic right or left ovaries as well 



° The spontaneous reversal of sex that frequently 

 follows removal of the dominant left ovary in the 

 young female chick is an example, and the basis 

 for this phenomenon lies in the predominantly 

 medullary ciharacter of the rudimentary right ovary 

 as described earlier. 



(Willier, 1933, 1939j. The same capacity 

 for self-differentiation has been demon- 

 strated under the more radical conditions of 

 isolation. Histologically undifferentiated 

 gonads of either species when cultured in 

 vitro differentiate into testes, or into right 

 and left ovaries of characteristic structure 

 (Wolff and Haffen, 1952a). In some cases 

 there is injury to the germinal tissue under 

 culture conditions; the gonads may show a 

 reduction in the number of germ cells, or 

 in some cases complete sterility, but other- 

 wise the structure is normal (Fig. 2.13). 

 Duck gonads seem to be more hardy under 

 conditions of culture than those of the chick, 

 and in general show better growth and liisto- 

 logic differentiation. 



2. Effects of Administering Pure Hormones 



As noted earlier, sex reversal in the gon- 

 ads of birds was not demonstrated experi- 

 mentally until \)uve hormones became avail- 

 able. The first successful experiments were 

 those of Kozelka and Gallagher (1934) ; 

 Wolff and Ginglingcr (1935) ; Willier, Gal- 



