70 LINKAGE 
ing over between the sex factor and the various sex 
linked factors can not be calculated, since in the sex 
that is heterozygous for the sex factor no crossing 
over has been observed. Sex linkage has been found 
Fic. 26.—Black Langshan female by Barred Plymouth Rock male. 
Compare with Fig. 30 (similar cross in Abraxas) for scheme of inheritance, 
which is the same in both. Substitute Black for lacticolor and Bar for 
grossulariata. 
in the moths Abraxas (Figs. 30 and 31) and Lyman- 
tria, in the fowl (Figs. 26, 27, 28, 29) (six factors), 
canary, pigeon, Drosophila (Figs. 9 and 10), fish, cat, 
man, and the plant Lychnis. In all, somewhat more 
than fifteen species show linkage. 
This number appears small in comparison with the 
