Sex Determination in Phylloxerans and Aphids 255 
whether the chromosome group is the same for the female-produc- 
ing and for the male-producing embryo. ‘The observations leave 
the point in doubt since no differences were found, but the num- 
ber of cases was not large. 
= e 
Be “Ps de 4: 
A B 3 D 
W 
Fig. IX B-E, equatorial plates of polar spindle of female egg; A, side view of same; I-W, equatorial 
plates of polar spindle of male eggs; F—H, side views of same. 
The female-producing winged form of the next generation con- 
tains a few large female eggs. The polar spindle in these eggs con- 
tains a group of six nearly equal chromosomes as seen in Fig. [X, 
A-E. Inthe polar spindle of the male egg of other winged indi- 
viduals there are also six chromosomes, but of very unequal sizes 
(Fig. IX, -W). There is one largest chromosome, almost twice 
