GENETICS: W. E. CASTLE 
35 
spending with the two views given for D. ampelophila in figures 1 and 2. 
The eight genes lie in four groups at the four apices of the figure, in groups 
of 2, 3, 2, and 1 respectively. The figure has a very definite and rigid form, 
for geometrical reasons. Three additional linkage relations should be known 
to determine fully the position of certain of the genes within their respective 
Y 
FIG. 4. MODEL SEEN AT RIGHT ANGLES TO FIGURE 3 
groups. These are magenta-hairy, glazed-rugose, and frayed-forked (or 
frayed-glazed), where the figures show connecting wires to be wanting 
Given these missing connections, the form of the model would be very fully 
determined in every detail. Any newly discovered sex-linked gene of D. 
virilis having been located with reference to three of these eight genes, its rela- 
