SEX REVERSALS 279 



eggs (Fig. 148). The eggs have been deposited and 

 fertilized and observed to develop. There can be here 

 no doubt but that a female has arisen after removal 

 of the testes, but whether the individual operated upon 

 is to be called a male or an hermaphrodite is perhaps a 

 question of definition. Personally, I should call the above 

 toad a male, and interpret the result to mean that a male 

 has been transformed into a female by removal of the 

 testes. It seems to me a matter of secondary importance 

 that the male toad carries an organ whose cells are poten- 

 tially capable of developing into egg-cells, for, in general, 

 even when sex is determined by a chromosomal mecha- 

 nism, there is no implication that under changed condi- 

 tions undifferentiated cells situated in that part of the 

 body where the gonads develop might not become egg- 

 cells even with the chromosomal complex that gives rise 

 to a male under other circumstances. In terms of genes, 

 this means that in the toad the balance of the genes is 

 such that under the normal conditions of development 

 one part of the gonad (the anterior end) begins to de- 

 velop into an ovary, while another part (the posterior 

 end) begins to develop into a testis. The latter overtakes 

 the former as development proceeds and holds its further 

 development in check. If the testicular end is removed, 

 however, this control is lost, and the cells of Bidder's 

 organ proceed to develop into functional eggs. Ponse, us- 

 ing eggs from a transformed male, obtained 9 sons and 3 

 daughters. Harms reared from a similar male 104 sons 

 and 57 daughters. If it be assumed that the male toad is 

 XY, then it is expected that the eggs of the transformed 

 male will be X and Y in equal numbers. If now, these are 

 fertilized by a normal male, the expected offspring will 

 be IXX-f 2XY-f lYY. The YY-individuals probably fail 

 to develop, lea^dng a ratio of two males to one female, 

 which agrees closely with the actual results. 



