SEX INHERITANCE 87 
found that both the female and the male have 56 
chromosomes, with no obviously unequal pair. 
Normally in Abraxas the sex ratio is about 1 to 
1. In one exceptional line this equality of sexes 
was not the rule. In this strain Doncaster found 
many females which gave only daughters, and not a 
single son. Other females of this line gave many 
daughters but also a few sons, while still others gave 
practically a normal 1 to 1 ratio. 
When Doncaster examined this line cytologically, 
he found that although the males were normal, with 
56 chromosomes, the females were aberrant, having 
only 55 chromosomes. 
In the maturation of the eggs of such a 55 chromo- 
some female, the odd chromosome went to one pole, 
so that one polar plate had 27 and the other 28 
chromosomes. Doncaster first thought that the odd 
chromosome went more often to the polar body than 
to the egg, and that eggs that eliminate the odd 
chromosome become after fertilization individuals 
with 55 chromosomes, that is, females — while the 
few that retain it become 56 chromosome individuals 
— that is, males. Later work showed that the egg is 
left with 28 as often as 27 chromosomes. This result 
upsets the earlier interpretation. 
In normal strains there is a W chromosome present, 
but since this W chromosome may be absent without 
effect upon the sex of the individual, as shown above, 
it must be regarded as functionless in determining 
sex, and in this sense it corresponds to the Y of 
Drosophila. This evidence proves that there is 
