February, '10] FELT : HOUSE-FLY 



25 



northwest corner is 2614 inches wide and 7I14 inches high. This door 

 was allowed to remain open throughout the season, and the entrance 

 of animals or children prevented by the use of a coarsely screened 

 (%-inch mesh) door having an interior clear space of 23x67 inches. 

 The building was so situated that August 24, at 8 a. m., rays of the 

 sun reached back to the base of the corner of station 8 and a little later 

 in the day would extend to the base of the pail at station 6. There 

 vras sufficient illumination under these conditions at station 18 so that 

 one experienced little difficulty in discerning objects located there. 

 Mackerel kits containing horse manure thoroughly sterilized by steam 

 were placed at stations 6, 12, 18 and 23. The vivarium was located 

 about 20 feet from one barn where a horse was kept, the manure from 

 the animal being thrown outdoors. There w^as another barn, where at 

 least two animals were kept throughout the summer about 40 feet 

 away to the southwest and another barn about 50 feet due east. This 

 latter had been occupied in previous years by six to eight horses, and 

 when the vivarium was constructed it was expected that an equal num- 

 ber of animals would be kept in the building throughout the summer. 

 Owing to a change of plans but one horse was kept in this barn, and 

 as a partial result of this change there have been considerably fewer 

 flies than in previous years. Furthermore, the excessively cool weather 

 continuing well into June greatly delayed the appearance of the 

 house-fly in numbers. Relatively cool weather continuing throughout 

 the summer has also served to prevent rapid breeding. This combina- 

 tion of causes has resulted in house-flies being much scarcer than 

 usual. 



Experiments. House-flies were becoming somewhat abundant June 

 23d and operations were commenced by placing mackerel kits nearly 

 filled with sterilized horse manure, at stations (see numbers on figure) 

 6, 12, 18 and 23. House-flies becoming more abundant the latter part 

 of July, another set of pails with horse manure was placed at the sta- 

 tions indicated above and, in addition, one just outside the door. 

 Rather abundant rains kept the last named pail nearly full of water, 

 and numerous Muscid larvee were observed in the contents the remain- 

 der of the season. House-flies entered the \'ivarium freely, being 

 rather numerous at station 23 and frequently working back to station 

 6. Muscid larvoe were in pails at both of these stations and one, which 

 may possibly have been a Musca, at station 12. Fruit flies, Drosophila 

 species, were observed in numbers July 21 at station 6, evidently being 

 drawn in part by swill placed there for the purpose of attracting flies. 

 This species was very numerous about the pail, alighting in numbers 

 on the walls above, but scarcely penetrating into the darker portions 



