Sex Determination in Phylloxerans and Aphids 345 
is little to show that these parthenogenetic females, prior to the 
reduction divisions, differ essentially from ordinary females. It 
is a fair inference perhaps, that in some cases at least the sexual 
female may contain dual possibilities. 
The spermatogenesis of the phylloxerans shows that two classes 
of sperms are produced and it is significant, I think, to find that the 
class of functional sperm corresponds to that class in other insects 
that is “female-producing.”’ This means only that this combina- 
tion gives rise to a female, not necessarily that the sperm carry 
female determinants. ; 
In fact the analysis of the results if based on the assumption of 
male and female determinants demands that the “ female-produc- 
ing sperm” carry the male determinant. Such sperm would intro- 
duce into the sexual egg those elements which, after being carried 
through one or more parthenogenetic generations, make possible 
the production of males. The only clue as to what these elements 
might be is found in the accessory chromosomes. ‘The following 
situation then develops: The accessories left in thesexual egg must 
be the female accessories; the functional sperm brings in the male 
accessories. It follows that the male-producing parthenogenetic 
egg must have eliminated its female accessories in order to pro- 
duce a male. There are then two (pairs of) female-producing 
chromosomes and one (pair of) male-producing. At the time of 
extrusion of the polar bodies in the male egg of the phylloxerans, 
the two female accessories must always be thrown out and the 
two male accessories retained. Conversely for the sexual egg. 
Extending the same reasoning to other insects with accessories it 
follows that the “female-producing” sperm contain the male 
accessories. Such sperm must fertilize eggs containing the female 
accessories and produce the heterozygous female. ‘The sperm 
without the accessory must fertilize an egg containing the male 
accessories and produce the homozygous males. ‘This means 
selective fertilization. 
Such seems to me to be at present the logical outcome of the 
assumption that the accessories are sex-determinants if their 
determination is a qualitative process. 
Several objections to this view have been already urged and 
