70 



THE AMERICAN NATURALIST 



[Vol. XLV 



00 Of 



But this last simplification is misleading, if the thesis 

 that I shall here maintain in connection with sex-limited 

 inheritance is correct; because the F's and the f's 

 omitted in the last case are supposed to be carried in 

 definite bodies, the chromosomes, which also carry other 

 factors than sex factors, and it is essential to indicate 

 their presence in some way in order that these other fac- 

 tors may have some means of transportation. 



In a recent paper on sex determination in phylloxerans 

 and aphids (1909) I discussed at some length different 

 theories of sex determination, and adopted provisionally 

 the view that the outcome is determined by a quantita- 

 tive factor. The present hypothesis is little more than a 

 further development of this same view, 2 but I hope in a 

 form more in accord with the Mendelian treatment of 

 the problem. Sex is still represented as the result of a 

 quantitative factor F (or f), but its relation to the male 

 factor is now expressed, for maleness is not assumed, as 

 before, to be no femaleness or less femaleness. Here, as 

 there, more of a particular factor turns the scale towards 

 femaleness in the first class of cases, and less of the fe- 

 male factor allows the scale to turn in the opposite direc- 

 tion in the second class of cases. 3 



2 In 1903 I suggested that in the case of the bee a quantitative factor 



a male. Wilson ( litnf,) has identified the quantitative factor with a special 

 chromosome and this interpretation ,.f the quantitative factor is here fol- 

 lowed. On Wilson's view the male condition is represented by the absence 



