No. 530] CONCEPTION OF PURE LINES 67 



used, in which the female is represented by two X's and 

 the male by one X: 



XX Female X ^ X 



XO Male X O 



"XX XO 

 female male 



The XO— 00 scheme applies, as before, to the case of 

 Abraxas and to poultry, and the XX— XO scheme to the 

 other class of cases. The latter expresses also exactly 

 what takes place in the chromosomes of those groups 

 where two classes of sperm exist (in relation to the X 

 element), as has been demonstrated by Stevens and by 

 Wilson. 



In both of these two latter schemes the production of 

 the female is ascribed to the presence of the chromosome 

 X, but in the first formula one X makes the female and 

 its absence stands for the male, while on the second 

 formulation two X's make the female, while one makes 

 the male. In one case XO is female and in the other XO 

 is male. Again we meet with the same paradox as in 

 the first two formulations. 



The chief drawback to these formulae is, in my opin- 

 ion, the absence of any character to stand for maleness. 

 Absence of femaleness does not appeal to me as a suffi- 

 cient explanation of the development of a male ; for the 

 male is certainly not a female minus the female char- 

 acters. 



Nevertheless, despite these objections I am inclined 

 to think that these two methods of formulation indicate 

 the direction in which we must look for an explanation 

 of the experimental evidence, and that they may be still 

 utilized provided we can so modify them that their in- 

 consistences can be made to disappear. 



It seems to me that if we are to succeed in bringing 

 sex into line with Mendelian methods we must be pre- 

 pared to grant that there are representative genes for 

 the male condition and others for the female; and we 

 must so shape our formula? that the female carries the 



