INTRASPECIFIC VARIABILITY. 



43 



The wing-vein indices, though known to be variable, nevertheless 

 offer valuable aids in the identification of species. How variable they 

 are may be gathered from the data in tables 5 and 6, which show the 

 results obtained from measurements of D. melanogaster from a number 

 of difTerent sources, and of D. melanica from Massachusetts. 



Total No., 70. M = 2.353 ± 0.017; a = 0.213 ± 0.012; V = 9.08 ± 0.58. 

 Table 6. — Indices of D. melanogaster and D. melanica. 



The number of branches on the antennal arista is usually given as a 

 specific character. It is also variable, as shown in table 7. In this 

 table the terminal portion of the main axis is counted as a branch, 

 so that an arista described as having five branches above and three 

 below would be entered here under "9." 



Table 7. — Variation in number of aristal branches. 



Species. 



Source of stock. 



10 



11 



12 



Total, 



D. melanogaster. 



D. immigrans . 

 D. funebris . . . 

 D. repleta ... 

 D. hydei 



Camp Jackson, S. C. 



Berkeley, Cal 



Arlington, Md 



Ann Arbor, Mich. . . 

 New York, N. Y. . . . 

 Lakeland, Fla 





 

 

 



12 

 13 



3 



17 

 4 

 

 6 

 2 



55 



20 



28 



1 











22 



3 



36 



12 













 

 4 

 17 

 

 





 

 

 10 

 

 



80 

 40 

 72 

 40 

 18 

 16 



Statistical constants for D. melanogaster, both races taken together: 



M = 9.042 ± 0.038; 0" = 0.610 dt 0.027; V = 6.74 ± 0.29. 



