226 
GENETICS: LANCEFIELD AND METZ 
Proc. N. A. S. 
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II 
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Figures 1 and 2 are diagrams; figures 3-10 are camera lucida drawings from fixed 
and sectioned material. 4 Figure 1. Chromosome group of Drosophila melanogaster 
female; X chromosomes represented in solid black. Figure 2. Chromosomes group 
of Drosophila willistoni; X chromosomes in solid black. Figures 3 and 4. Normal 
female groups of willistoni. Figures 5 and 6. Normal male groups of willistoni. 
Figures 7-10. XXY groups from non-disjunctional females of willistoni. 
Cytological Data. — The normal female chromosome group of Droso- 
phila melanogaster is represented diagrammatically in figure 1 and that 
of D. willistoni in figures 2-4. In melanogaster, as shown by Bridges 6 
('16) in his work on non-disjunction, the rod-like chromosomes are the 
X chromosomes. 3 These are represented in solid black in the diagrams. 
In the male of melanogaster this pair is asymmetrical, X being rod-like 
and Y J-shaped. In the male of willistoni no asymmetry is evident in 
any pair (figs. 5, 6). Otherwise the chromosomes of willistoni correspond, 
member for member, with those of melanogaster, except for the possible 
absence of the minute, spherical pair. 
