June, '16] PARKER: DISPERSION OF MUSCA DOMESTICA LINNAEUS 353 



breeding grounds) or inhibiting (e. g., low temperature, rain). Inciting 

 stimuli give rise to tropic reactions, movements to and from, and 

 consequently have a direct effect on distribution. Inhibiting stimuli 

 indirectly affect distribution, because of resulting periods of inactivity 

 on the part of the fly. 



3. These stimuli, both inciting and inhibiting, form a complex set of 

 external forces, each of which varies in intensity and duration. 



4. The adult life of the house-fly is essentially devoted to two 

 purposes, feeding and reproduction. Hence, it is evident that when 

 dispersion is considered as a problem of long periods or of seasonal 

 duration, that the stimuli from feeding and breeding areas are those of 

 the inciting stimuli which act most continuously and for the greatest 

 portion of a fly life and are the most important ones to control. 

 Temperature is a constantly present stimulus, but may be inciting 

 or inhibiting. 



5. When dispersion is considered for short intervals other stimuli 

 than those from feeding and breeding areas may assume greater 

 importance. These stimuli may be inciting or inhibiting and under 

 normal conditions have but minor significance as seasonal factors. 

 Cities or localities undoubtedly occur, however, in which unusual 

 physical or meteorological conditions are present with but shghtly 

 varying intensity during a complete season and consequenth^ what 

 would ordinarily be a stimulus of minor importance may become 

 one of major seasonal importance {e. g., strong wind blowing constantly 

 from some direction, long continued rain, etc.). 



6. By conducting dispersion experiments with a sufficiently large 

 number of flies for a sufficiently long time and by covering a sufficiently 

 large territory it seems likely that a limit for fly dispersion, under city 

 conditions, could be determined which would be of more or less 

 general application. The length of time would have to be at least 

 equal to that of the average length of house-fly life. 



BlBLIOGRAPHY 



1. Arnold, B. M. (1907). See "Report on the Health of the City of Manchester 



for 1906," by J. Niven. 



2. CoPEMAN, S. M., HowLETT, F. M. and Merriam, G. (1911). "An Investiga- 



tion on the Range of Flight of Flies." Reports to the Local Board on Public 

 Health and Medical Subjects, New Series, No. 53, pp. 1-9. 



3. Howard, L. O. (1911). "The House-Fly." pp. 51-56. 



4. Hewitt, C. G. (1912). "Observations on the Range of Flight of Flies." Re- 



ports to the Local Government Board on Public Health and Medical Sub- 

 jects, New Series, No. 66, pp. 1-5. 



5. Hodge, C. F. (1913). "The Distance House-Flies, Blue-Bottles and Stable- 



Flies may Travel over Water." Science, vol. XXXVH, pp. 512-513. 



