SEX INHERITANCE 137 
in Lychnis the male-producing pollen do not fertilize 
proportionately as many eggs in competition as they 
do when not enough pollen is present to fertilize 
all the eggs. Presumably the pollen-tubes do not 
grow as fast as those of the female-producing pollen. 
There is one situation that calls for special notice. 
In the WZ—ZZ type (moths and birds) the egg 
contains WZ in conjugation before the polar bodies 
are extruded. If it is only'a matter of chance 
which way this pair (WZ) lies on the spindle, then 
equal numbers of W-eggs and Z-eggs result after 
the polar bodies have been given off. But if the 
WZ pair should be placed so that the Z went out 
more often, more females would be expected; and 
if the W went out more often, then more males 
would result. Now in a few cases (Doncaster and 
Seiler) the W-chromosome is absent. In the egg 
of such a female there would be a “lagging” Z on 
the maturation spindle and if this tended to pass 
out (or to be lost) more often than to remain in 
the egg, the sex-ratio would be turned toward 
females. In fact any sex-ratio might result from the 
OZ type of individual. Moreover, once started, 
such an OZ line would perpetuate itself. In the 
case of the Y chromosome of the XX—XY type it 
makes no difference in the sex-ratio to which pole 
the X goes since both poles produce functional 
sperm, and the Y has disappeared in many cases. 
Another way in which sex-ratios are influenced is 
through the viability of the zygotes. In extreme 
cases, occurring in Drosophila all the offspring of a 
