June, '16] PARKER: DISPERSION OF MUSCA DOMESTICA LINNAEUS 34^ 



examined on August 26 contained one. In order to reach the Sales 

 Yards the flies had to cross a river several hundred feet wide. Fort 

 Keogh was very clean and sanitary. 



Evidence previously submitted showed that flies from breeding 

 grounds within the city which was liberally spotted with attractive 

 feeding and breeding areas, not onl}^ crossed it but 700 yards of open 

 country beyond. This indicates that not only are breeding grounds 

 outside a city of concern to its inhabitants, but that insanitary 

 conditions within a city may also concern outside residents. 



In respect to factors influencing dispersion across open country, the 

 writer is again of the opinion that the two big factors are the stimuli 

 from feeding and breeding areas, but with these differences; first, that 

 such areas are relatively of small size; second that they are much 

 farther apart; third, that the stimuli "thrown out" are weaker, and 

 fourth, that other active stimuli may exert a relatively greater influence 

 and act for relatively longer periods of time. Thus, in its existence 

 in nature as undisturbed by man's occupation, we are justified in 

 considering the house-fly as primarily a migratory insect. 



Concerning General Distribution, Time of Distribution and 



Numbers of Flies 



General Distribution. — From the data given on the maps it can 

 be seen that flies from the several release points become quite generally 

 distributed over the entire city and spread even beyond its limits. 

 An examination of the data in Table II gives arnple evidence on this 

 point. A trap placed at Station 214 for four days (July 24 to 28) 

 captured flies from the Sales Yards, City Dump and Laboratory; 

 one placed at Station 208 for four days (July 31 to August 4) captured 

 flies from the same three release points; one placed at Station 105 

 for three days (August 3 to 6) captured flies from the Sales Yards, 

 Laboratory and Washington School; one placed at Station 119 for 

 four days (August 6 to 10) also captured flies from these three release 

 points; one placed at Station 224 for four days (August 7 to 11) 

 captured flies from all four release points; one placed at Station 33 for 

 two days (August 12 to 14) captured flies from the Sales Yards, City 

 Dump and Washington School; one placed at Station 127 for three 

 days (August 14 to 17) captured flies from the Sales Yards, Laboratory 

 and City Dump and three placed at the State Industrial School 

 (Station 62), 700 yards beyond the eastern limits of the city, captured 

 flies from all points during a period of eleven days (August 9 to 20). 

 These illustrations are few in comparison to the data available, but 

 have been purposely selected to cover all sections of the city, thus 

 indicating the general distribution from each point of release. 



