PREOVIPOSITION PERIOD OF THE HOUSE FLY. 3 
was removed each day and examined carefully for eggs. Fresh horse 
manure was supplied each day, care being taken that the manure 
was not fly-blown before it was introduced into the cages. This was 
managed by taking fresh manure from the stables early in the morn- 
ing and keeping it in covered cans until used, and then examining it 
before introducing it into the cages. During midsummer the addi- 
tional precaution was taken of boiling the manure for one-half hour 
before it was put in the cages. When other media were used for 
oviposition the same precautions against previous infestation were 
taken. At the time of the daily examination of the cages, and at 
other times as opportunity offered, observations were made as to 
copulations. As a rule a regular routine of observations was fol- 
lowed out with each lot of flies as long as any of them remained alive. 
In a few cases, however, the flies were killed after the first deposition 
of eggs in order to provide cage space for the new lots of flies emerging. 
When, upon examination of the cages, it was found that eggs had 
been deposited, these were transferred, together with the medium, to 
small breeding boxes. These breeding boxes were of wood and very 
tightly made so that no cracks offered a chance for the escape of migrat- 
ing larve. Boxes of two sizes were used. When the number of eggs 
was small they were bred out in small boxes measuring 8 by 8 by 10 
‘inches, and for larger lots boxes measuring 12 by 18 by 12 inches were 
used. In one end of these boxes was an armhole 5 or 6 inches in 
diameter. Tacked carefully over this was a sleeve of black cloth of 
close weave. This was kept tightly closed with a rubber band when 
not in use. The top of each box was covered with a glass plate. 
Thus any flies could be seen as soon as they emerged. 
As soon after emergence as possible the flies were transferred from 
the breeding boxes to the cages described above. This was done 
by capturing them in vials introduced through the sleeve, or by con- 
necting the armhole of the breeding box with that of the cage by 
means of a glass cylinder. When the breeding box was darkened the 
flies soon found their way into the cage through the cylinder. Some- 
times the puparia were collected from a breeding box before any 
emergence had taken place and put into vials or pill boxes and covered 
with sand. These were put into cages until emergence had occurred. 
After the first lot of flies had emerged the remaining puparia were 
transferred to another cage to obtain a second lot, and so on until all 
had emerged. 
THE PREOVIPOSITION PERIOD. 
The preoviposition period was determined in some 70 experiments 
during the season of 1914. Table I summarizes the results of these 
experiments, most of which are based on Mr. Pomeroy’s notes but 
which include also some experiments by Mr. Webb and the writer, 
carried out during the autumn and winter. They have been arranged 
in the table in the order of the increasing length of the period. 
