336 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9' 



Total number of flies released, 387,877. 



Total number of flies recaptured, 1,056. 



Total number of stations used, 91. 



Total number of stations at which flies were recaptured, 78. 



(Traps were not recovered from 8 stations, hence liberated flies were- 



recaptured at 78 stations from a total of 83 from which flies were 



examined). 

 Combined total of days during which traps were placed, 680. 

 Longest distance at which flies were recaptured within city limits, 



2,333 yards. 

 Longest distance at which flies were recaptured, 3,500 yards (nearly 2 



miles). 



Stations at which flies were recovered from 1 release point only: 

 2, 3, 4, 5, 7, 8, 9, 10 (these traps were moved before it was possible 

 to make recaptures, except from Laboratory release point), 12, 17, 24, 

 25, 34, 35, 36, 37, 101, 103, 110, 111, 112, 113, 120, 122, 124, 128, 129, 

 212, 213, 223, 241, 242, total 32. 



Stations at which flies were recovered from 2 release points: 104, 

 107, 115, 1, 15, 19, 20, 21, 26, 28, 29, 30, 32, 38, 59, 64, 204, 205, 209, 

 215, 217, 218, 219, 222, 239, 240, total 26. 



Stations at which flies were recovered from 3 release points: 11, 18, 

 31, 33, 105, 109, 117, 118, 119, 121, 127, 165, 208, 211, 214, 220, 

 total 16. 



Stations at which flies were recovered from 4 release points: 62, 

 168, 216, 224, total 4. 



Possibilities of Error 



The methods used in counting and releasing show several possi- 

 bilities of error. What would at first sight seem a most potent source 

 was the fact that flies for release at the City Dump and Washington 

 School were captured at the Sales Yards about a hundred yards from 

 the Sales Yards release point and the possibility of capturing flies 

 stained with rosolic acid and afterwards releasing them again at the 

 two points mentioned is at once apparent. When the facts are con- 

 sidered, however, the danger of thus affecting the results becomes less 

 obvious. Table II shows that out of 150,000 flies captured in a trap 

 placed at the Sales Yards during two weeks (July 31 to August 13) 

 only 197 Sales Yards flies were recaptured; that is, approximately one 

 for every 750 released. The smaller Hodge traps were placed near this 

 large one and it is fair to assume that they recaptured stained Sales 

 Yards flies in the same ratio. Hence, since such flies were released 

 at the City Dump and Washington School there would have been 

 approximately 133 Sales Yards flies released at these two points. 



