744 
Journal of Agricultural Research 
Vol. XXI, No. io 
each of the other directions. The large number of marked flics taken 
in the lines of traps west and north as compared with those taken in the 
traps east and south strongly indicates that there was a tendency in this 
experiment also to travel with the wind, as the prevailing wind during 
the first nine days was from the south to east, and during the first five 
days the wind was almost constantly from the south and southeast. 
The respective number and percentage of house flies and screw-worm 
flies recovered in the different directions were as follows (based on total 
number of marked specimens of each species): West, 67 (45.89 per 
cent) and 104 (37.68 per cent); north, 50 (34.25 per cent) and in (40.22 
per cent); east, 21 (14.38 per cent) and 46 (16.67 per cent); south, 8 
(5.48 per cent) and 15 (5.43 per cent). All but one of the specimens of 
Ophyra and Sarcophaga were recovered in the west and north traps. 
The influence of traffic along the roads on dispersion would be prac¬ 
tically the same as in the first test; that is, the principal traffic was east 
and west of the point of liberation. Heavy traffic also passed between 
No. 3 and 4 north and 3 and 4 south. 
sex in relation to migratory tendency 
In this test it is noteworthy that not a single male house fly was 
recovered. With the screw-worm fly the percentage of females recovered 
was 75-3- This percentage was remarkably uniform in the different 
directions from the point of liberation, ranging from 71.7 011 the east line 
of traps to 76.9 on the west line. Considering the distance of dispersion 
of the males and females of the screw worm there is a slight indication 
that there was a greater tendency toward wide dispersion among the 
females than among the males. It may be worthy of note that the 
females appeared to enter the various traps in greater numbers during 
the early part of the recoveiy period than did the males. For instance, 
the percentage of males entering all of the traps during the first three 
days of the test was about 21, while during the remainder of the recoveiy 
period it was 45. This should not be construed as meaning that the 
males were necessarily slower in dispersion, but they may have displayed 
less eagerness to And food and lienee to become entrapped. 
RAPIDITY OP DISPERSION 
Comparatively few marked flies were recovered in the traps when 
emptied the first day after liberation. This was especially notable in 
the fourth ring of traps (3.75 to 5 miles from the point of liberation) 
where only a single specimen of Chrysomya macellaria was recovered. 
The recoveries the second day (July 13) were markedly larger than the 
first, this day giving the maximum daily catch (134) of C. macellaria for 
the period. This species seemed on this day to be generally distributed 
throughout the area, nearly all traps showing a marked decline in the 
