200 HEREDITARY CHARACTERS 



tion of any egg by any spermatozoon explains the numerical 

 quality of the sexes in the same way that it explains the 

 equal numbers of the two classes of offspring of an ordinary 

 Mendelian cross between a homozygote recessive and a 

 heterozygote. An obvious difficulty at once appears, how- 

 ever, in the parthenogenetic forms ; for here the partheno- 

 genetic females must bear both tendencies, since they, 

 sooner or later, produce males without fertilisation. We 

 need not enter into Correns's suggestions in regard to the 

 aphids and phylloxerans, since they are contradicted by 

 the facts of the spermatogenesis. In the case of the bee, he 

 adopts Beard's supposition that there are two kinds of eggs 

 sexual female-producing, which require fertilisation, and 

 parthenogenetic male-producing. In the latter the original 

 female tendency is replaced by the activation or setting 

 free of a male tendency previously latent. 1 A similar 

 explanation might be applied to the aphid, phylloxeran, 

 or daphnid. But does not such manipulation of the sexual 

 tendencies greatly weaken the force of the Mendelian inter- 

 pretation ? To me it seems that if the sexual tendencies 

 may thus be shifted back and forth between the active and 

 latent states, the interpretation loses most of its explanatory 

 value. 



" Can we then explain the difficulty in question by 

 reversing Correns's hypothesis, assuming the male to be 

 the homozygote, the female the heterozygote ? This is the 

 hypothesis of Bateson, who further suggests that different 

 species or groups may differ in respect to the sex that is 

 homozygous. The fertilisation formulas now become 



Egg ? + spermatozoon <$ = zygote ? ( <$ ) (female) 

 Egg c? + spermatozoon < = zygote $ $ (male). 



But new and even more serious difficulties now arise. If 



1 To understand this it must be borne in mind that Correns regards each 

 " active " sexual tendency (whether dominant or recessive) as accompanied by a 

 " latent " (not to be confused with a recessive) opposite tendency. Such a latent 

 male tendency in the female, upon becoming activated, would dominate the 

 female. 



