BIOLOGIC BASIS OF SEX 



use of extreme^; of temperature to induce 

 reversal of differentiation in the gonads of 

 anuran larvae (Witschi, 1929; Piquet, 1930; 

 Uchida, 1937 1 . The reversal is due primarily 

 to an unfavorable effect on the dominant 

 component, high temperatures causing cor- 

 tical degeneration in females and low tem- 

 peratures inhibiting medullary development 

 in males. Also, simple surgical interventions 

 or even pathologic injury may have the 

 same effect. Castration in certain cases re- 

 sults in complete reversal of sex through the 

 reactivation and renewed development of a 

 recessive gonad component left behind at 

 operation. In adult male toads removal of 

 the testes permits the organs of Bidder to 

 develop into ovaries, which may become 

 fully functional (Ponse, 1924). A compara- 

 ble case is found in the reversal of sex which 

 takes place in female chicks castrated soon 

 after hatching. Removal of the dominant 

 left ovary is followed by development of the 

 rudimentary right gonad, composed largely 

 or entirely of medullary tissue, into a small 

 testis. Finally, rare cases of partial or com- 

 plete sex reversal in adult hens, which oc- 

 cur as a result of pathologic destruction of 

 the functional ovary, appear to have the 

 same morphologic basis (Crew, 1923; for a 

 discussion see Domm, 1939 1 . 



But although sex differentiation in most 

 vertebrates ends in the complete dominance 

 of one sex component, remarkable devia- 

 tions from this plan are known in certain 

 groups and species. An extreme is found in 

 the prevalence of hermaphroditism, in vary- 

 ing degree, in many teleost fishes and in 

 cyclostomes (see ch. 17) which may be of 

 the juvenile type and temporary, or may 

 persist in adults. In toads the curious struc- 

 ture known as Bidder's organ is present in 

 adults of both sexes; it represents a local 

 region of the genital ridge in wliich medul- 

 lary cords are never formed and furtlier dif- 

 ferentiation does not occur. Since it corre- 

 sponds morphologically to the cortical 

 component of the gonad it retains through- 

 out life the potentiality of an ovary. This 

 condition is apparently possible in toads 

 because of the very low level of antagonism 

 in this genus. Stranger still is the situation 

 found in the female of certain insectivores 

 (the mole, Godet, 1949, 1950; the desman, 



Peyre, 1952, 1955j in which the medulla 

 of the adult ovary is testis-like and devel- 

 oped to a remarkable degree. Except during 

 the reproductive period it greatly exceeds 

 the cortex in bulk. Its cords are tubular in 

 form, resembling testis tubules, and a well 

 developed interstitium indicates an endo- 

 crine activity which is reflected in the strong 

 masculinization of the genital tract. The 

 clitoris is large and penis-like, and male ac- 

 cessory glands, absent or rudimentary in the 

 females of most mammals, are well devel- 

 oped. Another species in which the ovarian 

 medulla is highly developed, at least 

 throughout fetal life, is the horse (Cole, 

 Hart, Lyons and Catchpole, 1933). Thus 

 many patterns are found with respect to the 

 persistence of the heterotypic sex compo- 

 nent of the ovary and its final fate. 



B. SEX REVERSAL IN AMPHIBIAN GONADS 



1. Constitutional Differences and the Char- 

 acter of the Reversal Process 



Modern amphibians, far from being a 

 homogeneous group, are extremely diversi- 

 fied in structure and function and are often 

 highly specialized. Such diversification ob- 

 viously has had a long evolutionary history. 

 Correspondingly, the processes of sex re- 

 versal as evoked experimentally in amphib- 

 ian gonads, often follow very different histo- 

 logic and physiologic patterns in different 

 groups, species, or races. These differences 

 must rest ultimately on genetic constitution ; 

 more immediately they are predetermined, 

 in labile fashion at least, in the structural 

 and physiologic organization of the gonad 

 primordium which is in itself a complex sys- 

 tem. 



The organization of the early gonad may 

 vary greatly (according to species and ac- 

 cording to sex) with respect to the cortical 

 and medullary elements as laid down histo- 

 logically in the primordium — is the hetero- 

 tyi:)ic sex component of the primordium well 

 represented or is it quantitatively deficient 

 fiom the beginning? The subsequent be- 

 liavior of the heterotypic component is also 

 important— does it jiersist and regress slowly 

 over a considerable period of time or is its 

 existence transient? Furtliermore. how does 

 it react when the normal balance of the dif- 



