DISTRIBUTION OF THE CHROMOSOMES 201 
carrying both Z and W, and if such a ZW sperm 
fertilized a zero egg of the 55 chromosome female, a 
56 chromosome female would be produced. Don- 
caster actually found such a female among offspring 
from a cross of a female from the 55 chromosome 
race with wild type male, and he found also the 
genetic exceptions required on the assumption that 
this male was a WZZ form. 
