Sex Determination in Phylloxerans and Aphids 307 
THE CYTOLOGICAL EVIDENCE 
The recent cytological discoveries may be said to have revolu- 
tionized our ideas concerning the possibilities of sex determina- 
tion particularly within the group of insects, and more particularly 
within the hemiptera, to which group the phylloxerans belong. The 
discovery of the accessory by Henking in 1899, the further studies 
by Montgomery in 1898, by Paulmier in 1899, and by McClung in 
1899 and 1900 laid the foundation for the remarkable discoveries 
made later. In 1902 McClung suggested that the two kinds of 
spermatozoa might be connected with sex determination and inas- 
much as he observed that the number in the male was unequal 
he inferred that therefore the sperm containing the accessory pro- 
duced the male while the sperm without the accessory produced a 
female. On this assumption the female group should contain one 
less chromosome than the male. ‘The facts published in 1905 by 
Stevens and by Wilson showed, on the contrary, that the female 
contains one more, not one less chromosome than the male." 
Thus while McClung’s general inference proved true, when the 
necessary facts were obtained, the further question raised by him as 
to the relation of sex to the accessory proved to be the reverse of his 
assumption. 
The literature of the réle of the accessory in spermatogenesis has 
. been so often reviewed in recent years that there is no need to 
review it again. 
In regard to the phylloxerans, two conclusions of importance are 
deducible from the evidence. In one species, P. caryzcaulis, 
there occurs an early union of two pairs of chromosomes and it is 
probable that these are the accessories. Second, the evidence 
that two whole chromosomes are eliminated in the male rests on 
the observation of the number of chromosomes in the polar body, as 
well as the absence of two chromosomes in the egg after the 
extrusion of the polar body, and lastly on the inference that two 
chromosomes must have been eliminated in the male line in order 
that the behavior of the accessories in the spermatogenesis can 
be made to conform with their behavior in the rest of the insects. 
11 When a pair of idiochromosomes is present the female contains the larger. 
