CHROMOSOMES. 39 
VII. CHROMOSOMES. 
The chromosomes of various species of Drosophiline have been 
studied by Miss Stevens (1908), Bridges (1916), and Metz (1914, 1916). 
The two most striking general facts brought out by these studies are, 
first, that as a rule division figures are more easily obtained in ovarian 
tissue than in testicular; and second, that the two members of each 
pair of chromosomes commonly lie side by side at all cell divisions. 
This latter characteristic is found in most, if not all, other Diptera as 
well as in the Drosophiline. 
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Fia. 44.—Diagram of chromosome groups 
found in the Drosophiline (after Metz). 
Metz has described and figured the chromosome groups of a large 
number of species of the subfamily. He recognizes twelve different 
types, which are shown in figure 44, a diagrammatic representation 
made by Metz. The various types are represented by the following 
species: 
Type A. Chymomyza ameena. Type D. Drosophila immigrans. 
C. procnemis. Type E. Drosophila melanica. 
Mycodrosophila dimidiata. Type F. Drosophila cardini. 
Scaptomyza graminum.* D. ramsdeni. 
Drosophila busckii. D. repleta (hydei?). 
D. bromeliz. D. similis. 
D. flore. D. tripunctata. 
D. melanogaster.* D. virilis. 
D. nebulosa. Type G. Drosophila funebris. 
D. quinaria. Type H. Cladocheta nebulosa. 
D. robusta. Type I. Drosophila mulleri. 
D. saltans. Type J. Drosophila obscura. 
D. willistoni. Type K. Drosophila affinis. 
Type B. Drosophila earlei. Type L. Drosophila caribbea. 
Type C. Scaptomyza adusta.* 
Drosophila calloptera.* 
In types I, J, K, and L the male and female groups are both shown, 
and these obviously differ with respect to one pair—the sex chromo- 
