MENDELISM AND SEX 143 



contains two more chromosomes than the other 

 kind. And, moreover, he has shown that in Phyl- 

 loxera fallax this internal difference is correlated 

 with a difference in size, the egg which contains the 

 accessory pair of chromosomes being larger than 

 the one without. And he has further observed that 

 the large parthenogenetic egg produces females and 

 the small one gives rise to males. Now this difference 

 between the two kinds of eggs arises in the course of 

 maturation, for previous to this they both contain the 

 higher number of chromosomes. But at the forma- 

 tion of the polar body, twelve chromosomes remain 

 in the large egg, but only ten in the small one. It 

 is clear then, that in the former case there has been 

 no extrusion of the pair of accessory chromosomes 

 during the formation of the polar body, while in the 

 latter case they have been extruded into the polar 

 cell. In other phylloxera and in aphids only one 

 and not two chromosomes is thus extruded. 



We thus see that those parthenogenetic eggs 

 which are destined to give rise to males have one or 

 more chromosomes eliminated from them. We may 

 suppose this is also the explanation why the partheno- 

 genetic eggs of the bee produce males alone. They 

 apparently are all of one kind, and have had their 

 accessory chromosome extruded during their matura- 

 tion. They therefore carry the reduced number of 

 chromosomes characteristic of the male somatic 

 tissues. 



The next case of sex-inheritance we may consider 

 is that which results when the currant moth {Abraxas 



