136 
R. Ruggles Gates. 
half of the primary exceptions survive. The XXY females are 
fertile and can be used for further breeding. 
Non-disjunction also occurs in the male, giving XY and O 
sperm. The XY sperm would produce XXY daughters, like the 
XXY females above but with red eyes. They are therefore not 
exceptions, but will give exceptions in their offspring. Wilson (1909) 
observed three spermatocytes of Metapodius, another insect, in 
which X and Y went to the same pole in the reduction division. 
The XXY females give about 4% of secondary exceptions (i.e., 4% 
of daughters like the mother and 4% of sons like the father) when 
crossed with a male having other sex-linked characters. This was 
Eggs XX 
XY 
X 
Y 
Sperms, X 
Y 
XXX 
XXY 
XX 
XY 
exception 
XXY XYY XY YY 
(5) $ vermilion (6) <J vermilion (7) $ vermilion (8) dies 
exception 
at first supposed to be due to a factor for non-disjunction. The 
exceptions were afterwards found to be due to the presence of the 
Y. After further breeding experiments it was predicted that 
cytological examination of the daughters of an exceptional female 
would show the presence of an extra chromosome in half the 
daughters while the other half would be normal. This prediction 
was completely verified. 
Let us consider now what will happen in XXY females. 
Synapsis may take place between the two X chromosomes, leaving 
the Y unmated (homosynapsis), or it may be of the XY type 
(heterosynapsis). About 84% of the cases were formed by breeding 
