Sex Determination in Phylloxerans and Aphids 275 
tion that determines sex? ‘The chromosomal elimination being 
the consequence and not the cause of sex. Such interpretation 
would involve a profound alteration in our views of the relation of 
sex and chromosomes. It would mean, for one thing, that in 
ordinary forms there are other differences in the two kinds of sperm 
that are male and female producing than that of the number of 
chromosomes. ‘The female spermatozoon would not be female 
producing only because it contains one or two more chromosomes 
than the male, but, conversely, it contains these chromosomes 
because other changes have already been initiated that cause the 
accessory chromosome to move into that cell. Just as in the male 
ege the behavior of the sex chromosomes is discriminative—two 
entire chromosomes going into the polar body, so in the sperm two 
entire chromosomes go into the “female-producing” sperm. It 
seems to me the evidence may mean that there is a mechanism in 
the cell that is determinative in regard to sex factors; and that 
this mechanism has come to have associated with it particular 
chromosomes. 
The chromosomal relations, however, remain still a fact and a 
very extraordinary fact. It is hard to conceive that these relations 
have no connection with sex determination, even if we grant that 
changes take place before the differences in the number of the chro- 
mosomes occur that foreshadow the later sex differences. Why this 
extraordinary behavior in regard to the chromosomes if it is not con- 
cerned with the sex relation? It may be as injudicious to ignore 
the hehavior of the chromosomes; as to deny that antecedent 
events also connected with sex determination are operative. The 
evidence that we have at present seems to point to the conclusion 
that in the insects at least, the chromosomes are involved in the 
series of changes that determine sex; but may not the chromosomes 
be only a part of the process that leads to sex determination? The 
visibility of the chromosomal changes has caught our eye; the 
obscurity of the antecedent changes has caused them to be 
ignored; but in such a case as this one where a parthenogenetic 
cycle is introduced, the analysis shows that conditions antecede 
the chromosomal elimination—conditions also essential to sex 
determination. 
