86 SEX INHERITANCE 
lacticolor, but the lacticolors are females only. The 
lacticolor grandmother has transmitted her peculi- 
arity visibly to half of her granddaughters, but to 
none of her grandsons. 
In the reciprocal cross (Fig. 31) of lacticolor male 
by grossulariata female, the daughters are like their 
father (lacticolor), and the sons are like their mother 
(grossulariata). This is so-called criss-cross inher- 
itance. When the hybrids (F;) are inbred, they give 
lacticolor males and females and grossulariata males 
and females in equal numbers. 
Sex linked inheritance, as shown by the foregoing 
results, becomes intelligible if the factor for lacticolor 
is carried by the chromosome Z. Its occurrence in 
Z is indicated here by writing an | inside the circle 
which represents that chromosome, while the allelo- 
morphic character carried by the Z of the grossu- 
lariata individual is indicated by writing L in the 
circle. The W chromosome is indicated by the 
blank circle. The two cases then work out as shown 
in the diagrams. 
The preceding analysis shows that the genetic 
evidence calls for a mechanism in-which the female is 
heterozygous for sex, since those of her eggs which 
carry the factor for grossulariata all develop into 
females, the others into males. In the case of 
Abraxas there was for some years no positive cyto- 
logical evidence in support of this view. Fortunately, 
the cytological side is now in a much better position 
owing to the work of Doncaster and Seiler. 
Doncaster examined Abraxas cytologically, and 
