496 T, H. MORGAN 
searcely justified inmaking thisassumption even although by doing 
so we may seem to give an attractive explanation of the splitting 
into the male and female lines. 
Other combinations will suggest themselves but offer no advan- 
tages I believe over the one that I have suggested. 
COMPARISON BETWEEN PHYLLOXERA CARYAECAULIS AND 
PHYLLOXERA FALLAX 
It may be worth while to compare briefly the conclusions 
reached for P. caryaecaulis with the results described in my former 
paper for another species, P. fallax. The latter has twelve chro- 
mosomes in the equatorial plate of the egg laid by the stem- 
mother. After the extrusion of the polar bodies I have described 
twelve chromosomes as the number for the cells of the embryo. 
If as in P. caryaecaulis there are two pairs of X’s present that 
are united this number would still be found, but if this view were 
correct for the male line we should expect to find six in the male 
spermatocytes of which one is double. Five should divide equally 
and the double one should lag with or without showing its double- 
ness at this time. In reality only four divide equally and two 
whole chromosomes that were separate in the equatorial plate 
of the spermatocyte come near together and become the lagging 
chromosomes of this division. There can be no question of their 
relations in the spermatocytes since the chromosomes are per- 
fectly distinct and hundreds of such stages have been studied. 
It seems necessary therefore to recast this first view and to reéx- 
amine the facts. In fig. Il; A-—F of my paper six chromosome 
groups of polar spindles of male- and female- producing eggs are 
drawn. Of these groups three show twelve chromosomes, two 
show eleven, and one is doubtful. In fig. Il a; C-T there are nine 
groups showing twelve chromosomes, one is doubtfully twelve 
or eleven, one shows eleven, and one shows ten. These are all 
from winged individuals. These retain their eggs for some days 
and several ripe eggs are found in the body of each individual, 
while the wingless individuals, which have replaced largely the 
winged in this species, bring to maturity only one egg at a time 
which is laid as soon as it is ripe. It is therefore more difficult 
