112 



BIOLOGIC BASIS OF SEX 



many species as complete if somewhat rudi- 

 mentary canals. In amniote embryos, on the 

 other hand, the ducts of the genetically re- 

 cessive sex are typically transient struc- 

 tures. Sexual differentiation consists in the 

 retention of one sex duct with development 

 of its derivative structures, whereas the 

 other either disappears completely or sur- 

 vives only in a more or less vestigial condi- 

 tion (Fig. 2.22B). Under these circum- 

 stances experimental reversal of sex, to be 

 successful, must be properly timed with re- 

 spect to the state of development of the 

 heterotypic duct. Once regression has been 

 determined it is impossible to preserve the 

 duct. 



1. The Miillerian Ducts: the Effects of Fe- 

 male Hormones 



The effects of female hormones, whether 

 produced by grafted ovarian tissue or ad- 

 ministered in pure form, may be stated gen- 

 erally as follows: in female subjects as a 

 rule they accelerate sexual differentiation, 

 inducing a precocious hypertrophy of the 

 Miillerian ducts which with large doses may 

 become extreme. In males female hormones 

 cause persistence of the Miillerian ducts fol- 

 lowed by differentiation in varying degrees 

 depending on timing of treatment, dosage, 

 and the special status of the duct in the 

 species under consideration. There are many 

 deviations from this pattern, however, aris- 

 ing in part from basic group or species dif- 

 ferences and in part from the many experi- 

 mental variables." 



In most amphibians the IVIiillerian ducts 

 of both sexes respond readily to sex hor- 

 mones during larval life. In Triturus {Tri- 

 ton) , after castration, both sex ducts remain 

 indefinitely in a more or less undifferenti- 

 ated condition, thus providing an ideal basis 

 for sex reversal. Grafting gonads into cas- 

 trates of either sex readily induces differen- 

 tiation of the appropriate duct (de Beau- 

 mont, 1933). Furthermore, in the males of 

 various species which have undergone com- 

 plete sex reversal the later development of 



" For reviews and references to a large literature 

 covering amphibians, birds, and mammals see 

 Humphrey, 1942; Wolff, 1938; Willier, 1939; Rav- 

 naud, 1942; Greene, 1942; Moore, 1947; Jost, 1947a, 

 1948a, 1955; Ponse, 1949; Burns, 1949, 1955b; Stoll, 

 1950. 



the ]\liillerian ducts is always in accordance 

 with the altered sex of the gonad, and the 

 ducts may eventually become completely 

 functional (see e.g., Humphrey, 1942; Ponse, 

 1949; Gallien, 1955). The reaction of the 

 Miillerian ducts to female hormones (estra- 

 diol, estrone) varies in different species and 

 is greatly influenced by the stage at which 

 treatment occurs and by dosage as well. In 

 Ambystoma the ducts show a marked hy- 

 pertrophy in females and the response in 

 males is almost as great. The backward 

 growth of the incomplete ducts is also ac- 

 celerated (Burns, 1938a; Foote, 1941). 

 Large doses, paradoxically, may arrest the 

 backward extension of the duct (as do male 

 hormones, q.v.) but the part already laid 

 down becomes greatly hypertrophied (for a 

 summary see Gallien, 1955). 



The effects of the female hormone in bird 

 embryos are particularly striking (Wolff, 

 1938, 1950; AVillier, 1939; Gaarenstroom, 

 1939; Stoll, 1948). In male embryos both 

 oviducts persist and hypertrophy as does 

 also the right duct of the female, which nor- 

 mally undergoes involution (Figs. 2.23 and 

 2.12). Once established these effects are per- 

 manent, development continuing even after 

 hatching (Wolff, 1938). However, the period 

 of susceptibility to the hormone is limited. 

 Retention and permanent development can 

 be assured only by treatment up to the 

 seventh day of incubation (this is the so- 

 called "stabilization effect" of Wolff) ; later 

 treatment is without effect for the preserva- 

 tion of the ducts, irreversible changes having 

 occurred which determine their regression 

 with finality (Wolff, 1953b). The hormone 

 of the embryonic ovary has the same effects. 

 Ovaries grafted into the body cavity of 

 male embryos cause persistence and devel- 

 opment of\he oviducts (Wolff, 1946). The 

 effect of the hormone appears to be a direct 

 one since it occurs independently of any ef- 

 fect on the gonads. 



In mammalian embryos the effects are in 

 general similar, but marked species differ- 

 ences have been found. Female hormones 

 cause accelerated development of the Miil- 

 lerian duct derivatives in females, and with 

 high dosages oviducts, uteri, and vaginal 

 canals all show great hypertrophy. In male 

 embryos the ducts are frequently retained 

 and also differentiate regionally into ovi- 



