DISTRIBUTION OF THE CHROMOSOMES 197 
results showed that the exceptions could be explained, 
if, occasionally, the two X chromosomes failed to 
disjoin in the reduction division, both passing out of 
some of the eggs of the white-eyed mother into the 
polar body, or, conversely, both remaining in the egg. 
If the two white-bearing X’s should remain in the egg 
then such an egg fertilized by a Y sperm would give 
rise to a white-eyed daughter. Likewise the no-X 
egg fertilized by the X sperm of a red-eyed male 
would give a red-eyed son. The white daughters 
would, as just shown, contain two X’s and one Y 
chromosome, unlike ordinary daughters, which con- 
tain. two X’s only. Since in these females there are 
three sex chromosomes instead of a pair, at the 
reduction division two must pass into one cell and 
one into the other. This division might take place 
nf ; XY xX Y d XX tj 
in four ways: Yo yy xx and (representing 
the egg below and the polar body above in each 
case). The first two types of reduction, depending 
on a more symmetrical pairing of the chromosomes, 
might be more frequent than the other two types. 
There would then be four types of eggs—a large 
number of X and XY eggs, and a few XX and Y eggs. 
Let us suppose that an XX Y white femaleismated toa 
red male. The progeny produced by the X bearing 
sperm would be: 
x XY Xe. XY 
Q red Q red missing G red 
