42 THE NORTH AMERICAN SPECIES OF DROSOPHILA. 
times, so that accidental environmental differences have been reduced 
toa 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 (V) 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— 
TUTTI STREET Ge aren 100 
Onion 2 o Oop Oli flies 
Drosophila immigrans: 
INORWAY ee eee Sk eee Catone 0/0 109 VSSu ee O On Oo 264} 0.8 
Attleboro wiViasss eee ONO 84 103 | 0; 0/0] 0 187 | 0.0 
IWihitesP lain s YIN) cue c ueleiees nel Ole a (05) 64;2/;1;0)]0 143 |) (2a8 
Statenelslangd Neve coat) Meyer ks ie val 89 1 Sloe Glin Wale aeslia a 213) oe2 
Staten wsland"@Now2) eee Ona O 72 64;1/0/]0)] 0 LSC inOea 
J Ned take soya yy Js (C0 Bn coche ols os Oieeeet os Oe 0; 0 105 OZ Ma alecin ieee EO 216} 4.2 
Gakeland shaver mas oe ee Set O 103 124 112 | 4 caste 248 | 9.7 
HO RCo re) (GUAR ea et gn Pe DEER oe Dalia 637 724 126 | 8 | 8 | 1 | 1,408 | 3.7 
Drosophila melanogaster: 
Randolph wiNewoe a sisetarnstoe es cians 0| 0 182 140/;9/|}3)]0);0 334 | 3.6 
HalmouthsVlasssee en cera cals ae 0; 0 100 OMG ie een ek 213 | 6.6 
NWihnteve aim saan Morehsuen oy eee senso Matis 128 147|2);0/]0) 0 273 OW 
(Baltimore Midis eae. emt gy. 0; 0 185 144}1/;)0;|0),0 330] 0.3 
CampidacksonyiS.G sense ale us 0; 0 112 1433) 2a ea sO 259} 1.9 
moehesterse Mann ees ase cone ot ne 0} 0 116 94; 1/0;]0)] 0 211 Or 
Berkeley aC aly. Sere Maciel ORO 115 Si] OR) 15) 408/20 LO Fea VOLS 
Malkeland blac, es ays naval te 0| 0 176 AZO} Mealeet | O20 348 | 0.6 
FARO Gallo Mega Lareen eee ssuh iee Wall dle do A) ON EAA OZON 22 NT1OR sZt iO 1.8 
Drosophila simulans: 
Cold Spring Harbor, N. Y........ 0/0 0/0) 0 
Statemilslancdea Ney acl nin ate 6 Lino 1 On 
ROChEStervivlInnee) oes eee ee 0/0 Oats yO 
KoushlaisAlacn oreo 2h oily ais anidy: 0; 0 0'0;0 
Lakeland, Fla.. 0/0 1/01] 0 
ol Noy es Beata na LAMY 3 Wig Nan AO I ON 1/0 aon inO 
Drosophila affinis: 
ING waVionkcaNceN incite cal ores 0; 0 NPC) 
Drosophila busckii: 
INGOT WB Vieni oer he Se ease Rate 0/1 0; 0/0 
Chymomyza procnemis: 
Makeland lasers yar feiss aes 0/0 On O50 



TABLE 4.—Statistical constants derived from table 3. 
(M = mean; o = standard deviation; V = coefficient of variation.) 
Species. M o V 
D. immigrans..............| 4.034 + 0.034 0.228 + 0.003 
D. melanogaster............] 4.016 + .003 146+ .002 
1D Mircrbaay bb Ey of ADU NM Vanna a 4.002 + .00004 .002 + .00003 


