756 
Journal of Agricultural Research 
Vol. XXI, No. io 
an index might be worked out and thus the difference in position equal¬ 
ized and the normal dispersion of the marked specimens be determined 
more accurately. This matter upon study became so complicated and 
so many unknown factors entered that it was dropped. It was finally 
concluded that a comparison of the relative positions might be made by 
computing in the form of percentage the relation between each of these 
principal species in the catches in the different traps and the total catch 
of each of the species in all the recovery traps. And again the percentage 
of marked flies of the two species in each trap as compared with the total 
marked flies of each species recovered in all traps was computed. 
These two percentages—the percentage of total house flies and per¬ 
centage of marked house flies taken in each trap—should approximate 
each other in size if all other factors such as distance, direction, etc., 
were eliminated. The same is true of the screw-worm fly. On the other 
hand, if the difference in these percentages is great, we must conclude 
that some other factor than mere local environment of the trap is domi¬ 
nant. These data are presented in Table IX and figure 3. 
Table IX. Weight and proportion of catch of Musca domestica and Chrysomya macel- 
larta compared with number and proportion of these species among marked specimens 
recovered in third test at Dallas, Tex. 
Trap No. 
Total 
weight 
M° do¬ 
mestica 
and C. 
macel- 
laria 
caught. 
Weight 
of 
M. do¬ 
mestica 
caught 
in 
trap. 
Per¬ 
cent¬ 
age of 
M. do¬ 
mestica 
com¬ 
pared 
with 
total 
in 
trap. 
Weight 
of C. 
macel- 
laria 
caught 
in 
trap. 
Per¬ 
cent¬ 
age of 
C. 
macel- 
laria 
com¬ 
pared 
with 
total in 
trap. 
1 west. 
Gm. 
368 
Gm. 
109 
20.6 
Gm. 
259 
70.4 
2 w r est. 
674 
262 
38.9 
412 
61.1 
3 west. 
242 
181 
74-8 
61 
25. 2 
4 west. 
752 
596 
79- 2 
56. 6 
156 
20. 8 
1 north. 
316 
179 
137 
43-4 
2 north. 
283 
238 
84.1 
45 
15- 9 
3 north. 
361 
333 
92. 2 
28 
7.8 
4 north. 
548 
120 
21. 9 
428 
78.1 
1 east. 
397 
104 
26. 2 
293 
73-8 
2 east. 
174 
57 
32-8 
117 
67. 2 
3 east. 
583 
446 
76-5 
137 
23- 5 
4 east. 
677 
72 
10.6 
605 
89.4 
1 south. 
202 
86 
42.6 
116 
57- 4 
2 south. 
520 
291 
56. 0 
229 
44.0 
3 south. 
196 
121 
61. 7 
75 
38.3 
4 south. 
327 
121 
37-o 
206 
63.0 
Total... 
6,620 
3 > 3 i 6 
3*304 
Per¬ 
cent¬ 
age of 
M. do¬ 
mestica 
in each 
trap 
com¬ 
pared 
with 
total 
M. do¬ 
mestica 
in all 
traps. 
Num¬ 
ber of 
marked 
M. do¬ 
mestica 
caught. 
Per¬ 
cent¬ 
age of 
marked 
M. d o¬ 
mestica 
in each 
trap 
com¬ 
pared 
with 
total 
marked 
M. do¬ 
mestica 
in all 
traps. 
Per¬ 
cent¬ 
age of 
C. 
macel- 
laria in 
each 
trap 
com¬ 
pared 
with 
total 
C. 
macel- 
laria 
in all 
traps. 
Num¬ 
ber of 
marked 
C. 
macel- 
laria 
caught. 
Per 
cent- 
age of 
marked 
C. 
macel- 
laria in 
each 
trap 
com¬ 
pared 
with 
total 
marked 
C. 
macel- 
laria 
in all 
traps. 
3-29 
3 
4-35 
7.90 
1 
1-45 
5-46 
2 
2.90 
17.97 
3 
4-35 
5-40 
15 
21.74 
7.18 
13 
18.84 
10.04 
5 
7.24 
3-62 
0 
0.00 
3-14 
2 
2.90 
1.72 
0 
0.00 
13-45 
4 
5.80 
2.17 
2 
2.90 
2-59 
10 
14.49 
8.77 
9 
13.04 
3-65 
0 
0. 00 
3 - 6 s 
0 
0. 00 
48 
7.84 
21 
12.47 
4 
1.84 
8 
4. 72 
38 
4-15 
7 
1.36 
0 
•85 
28 
12.95 
3 i 
8.87 
13 
3-54 
6 
4 - M 
5 
18.32 
38 
3 -Si 
13 
6- 93 
3 
2. 27 
9 
6. 24 
100.00 
69 
100.00 
27-2 
100.00 
17.64 
7. 72 
1.47 
2.94 
13-97 
2 - 57 
o. 00 
10. 28 
11.40 
4 - 78 
2. 21 
1. 84 
13-97 
4 - 78 
1.10 
3 - 31 
99.98 
