754 
Journal of Agricultural Research 
Vol. XXI, No. io 
Three of the four specimens of Ophyra aenescens were taken on the 
third day following release and the other on the fourth day. This species, 
which is ordinarily thought of as having little power of flight, has shown 
rather remarkable powers of dissemination in this instance. 
RELATION OF SEX TO DISPERSION 
The proportion of the sexes of flies released, based on examination of 
a considerable number of specimens killed at the time of release, was: 
Males, Musca domestica 25.6 per cent, Chrysomya macellaria 15.6 per cent, 
Phormia regina none, Lucilia sericata none, Ophyra spp. none, Sarcophagi 
spp. 22.2 per cent. It will be noted by referring to Table V that the per¬ 
centage of male M. domestica recovered (13) was not greatly different 
from the percentage (15.6) released. It is rather strange that one-half 
of the Ophyra recovered were males, while no males were noted in the 
material examined at the time of liberation. 
Referring to Musca domestica, the proportion of males to females 
increased from the nearer circle of traps (6.7 per cent) outward to the 
third circle (27.3 per cent), but no males were caught in the outer circle. 
This does not indicate that this sex is more limited in distance of dis¬ 
persion, since only 5 specimens were taken in the outer circle and the 
proportion of males to females was so small that the chance of re¬ 
covering any among that number was meager. The maximum distance 
of flight of any male house fly was 7.2 miles, one specimen being recovered 
in No. 3 east. The proportion of sexes of this species in the different 
directions was about the same (Table VI), ranging from about 10.6 per 
cent males in the traps to the south to 15.2 per cent in the traps to the 
north. 
In the case of Chrysomya macellaria the proportion of males to females 
varied considerably in the rings of traps at different distances, but not 
in a way to show any relation between sex and distance. The per¬ 
centage of males in the first ring of traps (4.5 miles) was highest (14.8) 
and in the third ring lowest (none). The same erratic results are also 
apparent in the proportion of sexes in different directions, but the average 
percentage of males taken in the traps in the different directions is not 
very different, ranging from 7.4 in the west line of traps to 144 in the 
east line. 
RELATION OF POSITION OF TRAPS TO THE RECOVERY OF MARKED FLIES 
At tlie outset in these dispersion studies it became apparent that 
the environment of the recovery traps had a marked effect not only on 
the size of the catch but on the proportion of the species. In other 
words, certain situations occupied by recovery traps were preeminently 
house-fly situations while in others the blowflies dominated. As an 
illustration the results in the case of traps No. 3 and 4 north may be 
