SEX-REVERSAL IN PARABIOTIC TWINS. 143 



to those reported by Burns (1925) in Amblystoma. This author 

 did not find that the male sex predominates or even that sex- 

 transformation decreases the growth of the involved gonads. 

 Furthermore, he supposes that the change of sex takes place 

 before the time of sex-differentiation. Let us consider the latter 

 point with respect of the present experiments with R. sylvatica. 



FIG. 5. Parabiotic twins 8841 (R. sylvatica). Left larva, 38 mm. total length. 

 68 days after operation. Female changing into male. Transverse section through 

 one of the gonads, showing inhibition of growth, disintegration of the germinal 

 epithelium and formation of the testis in the center of the gonad. mig., germ cells 

 migrating into the sex cords. X 444. 



Supposing there were such an early sex-reversal in the frog 

 twins, then the number of one-sexed pairs ought to be increased 

 at the expense of the two-sexed ones. However, the statistical 

 evidence is against such an assumption. There were found the 

 following combinations: 



cf c^ 16 



cT 9 17 (seven of the females undergoing sex-reversal) 



9 cf 10 (four of the females undergoing sex- reversal) 



9 913 



