2 BULLETIN 345, U. S. DEPARTMENT OF AGRICULTURE. 
1914 at New Orleans, La., at which place Mr. T. E. Holloway rendered 
great assistance. During the summer of 1914 an extended series of 
experiments was carried out by Mr. A. W. J. Pomeroy. After the 
severance of his connection with the bureau at the end of October 
the experiments which he had under way were continued during the 
fall by Mr. J. L. Webb, and during the winter months the writer 
continued the work in the greenhouses of the Arlington experiment 
farm of the Bureau of Plant Industry. 
METHODS USED IN THE PREOVIPOSITION EXPERIMENTS. 
In the experiments to determine the length of the preoviposition 
period (i. e., the time between the emergence of the adult fly and the 
first deposition of eggs) laboratory-bred flies were used. The breed- 
ing was carried out in a systematic way, and several strains or “pure 
lines’? were followed out through five or six generations. Most of 
the strains were started from a small number of larve or pupe found 
in manure piles, and the first flies to emerge from material thus col- 
lected were used as the parents of the strain. In one case, however, 
a strain was started from a pair of flies taken in coitu on July 25, 
1914. Eggs were deposited on August 2, and breeding of this strain 
was continued through six generations. 
The adult flies were kept in small cages. A type of cage found 
very satisfactory for this work was 22 inches high by 12 inches square. 
The framework was of soft pme 1 inch square. The top, bottom, 
and three sides were covered with bronzed screen wire, 16 mesh per 
inch. The fourth side, or front of the cage, was covered with screen 
wire about 8 inches down from the top. Below this was a board 
about 8 inches wide, in which was cut an armhole 5 inches in diame- 
ter. A sleeve of closely-woven black cloth was tacked over this. 
Below the board was fitted a drawer 4 inches deep, in which food 
and material for deposition were kept. Cages of this size were easily 
and quickly handled, and any part of the interior of the cage could 
be easily reached through the armhole, the sleeve preventing the 
escape of any flies during manipulations. The sliding drawer at the 
bottom of the cage made it possible to remove the contents and exam- 
ine them for eggs without permitting any flies to escape. These cages 
were kept on the shelves of a screened insectary and were protected 
from the direct rays of the sun most of the day, but were freely 
exposed to air currents and to the outdoor conditions of temperature 
and humidity. 
Flies were transferred to these cages soon after emergence and 
supplied with food and media for oviposition. The cages were 
examined daily; any dead flies were removed and the sex noted at 
the time of removal. In this way at the end of the experiment the 
total number of males and females was summed up, and the length 
of life of each fly in the lot was known. The manure or other medium 
