42 



THE NORTH AMERICAN SPECIES OF DROSOPHILA. 



times, so that accidental environmental differences have been reduced 

 to a minimum. Table 4 gives the results of a statistical treatment of 

 the totals for the three species D. immigrans, D. melanogaster, and 

 D. simulans. A comparison of the coefficients of variation (F) shows 

 that D. immigrans is more than 100 times as variable for this character 

 as is D. simulans. D. melanogaster is only slightly less variable than 

 is D. immigrans. The other species, for which little data are available, 

 have not been worked out in statistical form. 



Table 3. — Frequencies of various numbers of dorsocentrals. 



Stock from- 



c? 



& 



& 



9 & 



Total. 



Ex- 

 tras 

 per 

 100 

 flies. 



Drosophila immigrans: 



Norway 



Attleboro, Mass 



White Plains, N. Y 



Staten Island, N. Y 



Staten Island (No. 2) . . . . 



Arlington, Md 



Lakeland, Fla 



Total 



Drosophila melanogaster: 



Randolph, N. H 



Falmouth, Mass 



White Plains, N. Y 



Baltimore, Md 



Camp Jackson, S. C 



Rochester, Minn 



Berkeley, Cal 



Lakeland, Fla 



Total 



Drosophila simulans: 



Cold Spring Harbor, N. Y 



Staten Island, N. Y 



Rochester, Minn 



Kushla, Ala 



Lakeland, Fla 



Total 



Drosophila affinis: 



New York, N. Y. 



Drosophila busckii: 



Norway 



Chymomyza procnemis: 



Lakeland, Fla 



109 

 84 

 75 

 89 

 72 

 105 

 103 



637 



182 

 100 

 128 

 185 

 112 

 116 

 115 

 176 



1,114 



97 



116 



73 



64 



143 



493 



101 



91 



50 



153 

 103 



64 

 114 



64 

 102 

 124 



2 

 

 2 

 4 

 1 

 5 

 12 



264 

 187 

 143 

 213 

 137 

 216 

 248 



724 



26 



1,408 



140 

 101 

 147 

 144 

 143 

 94 

 81 

 170 



334 

 213 

 278 

 330 

 259 

 211 

 197 

 348 



1,020 



22 



10 



2,170 



86 

 79 



108 

 84 



115 



472 

 60 

 71 

 55 



183 

 197 

 182 

 148 

 259 



969 

 163 

 163 

 105 



0.8 

 0.0 

 2.1 

 5.2 

 0.7 

 4.2 

 9.7 



3.7 



3.6 

 6.6 

 0.7 

 0.3 

 1.9 

 0.5 

 0.5 

 0.6 



1.8 



0.0 

 0.5 

 0.5 

 0.0 

 0.4 



0.3 

 1.2 

 0.0 

 0.0 



Table 4. — Statistical constants derived from table 3. 

 {M = mean; a = standard deviation; V = coefficient of variation.) 



