12 BULLETIN 345, U. S. DEPARTMENT OF AGRICULTURE. 
or observations in support of his statement that the fly repeats the 
process of egg laying at intervals of 10 to 14 days till four batches 
have been laid. The largest number of eggs per deposition in these 
experiments was 96 and the smallest 25. 
Recent experiments have placed the knowledge of the preovi- 
position period on a more complete basis and have shown that the 
period is considerably shorter than was previously thought to be 
the case. Dr. C. G. Hewitt publishes the results of experiments per- 
formed by him in England in 1907, in which the period was found to 
be 14 days. Griffith (1908) states that the adult fly can begin to 
lay eggs 10 days after emergence. Bogdanow (1903) publishes the 
results of some breeding experiments with the house fly. In a table 
given in his article it appears that in one experiment the first flies 
emerged on August 12 and the first eggs laid by these flies were found 
on August 18—a preoviposition period of 6 days. 
COPULATION. 
Observations on the copulation of flies were necessarily not con- 
tinuous, but of chance observations there were a large number, and 
they show that copulation may occur as early as one day after emer- 
gence. There are three records oi copulations taking place on the sec- ~ 
ond day atter emergence, and 14 records of copulations on the third 
day after emergence. ‘The greatest number of records fall on the third 
to sixth days, inclusive. Copulations were observed as late as the 
twenty-sixth day, and in an experiment during the winter, when a 
lot of flies was kept in a stable where the air temperature ranged 
from 30° to 60° F., one copulation was observed on the forty-seventh 
day after emergence. The air temperature at the time was 55° F. 
During the autumn a number of copulations were observed taking 
place when the air temperature was 55° F., but no sexual activity 
was ever seen at temperatures lower than 55°. 
LONGEVITY. 
As stated, the daily routine of observations on the various lots of 
flies included the removal of dead flies and the recording of their sex 
and length of life. The experiments during the summer and fall of 
1914 include records of some 3,000 flies. The longevity of these 
flies varied from 1 day to 54 days. The arithmetical mean of all 
these records was found to be 19+ days. This may perhaps be 
taken as the average for both sexes at all seasons. In midsummer 
the length of life is often much less and during the spring and autumn 
months is considerably more. In one hibernation experiment, in 
which flies were kept in a stable at temperatures varying from 30° 
to 60° F., afew lived aslong as 70 days. This record was not included 
in calculating the mean longevity. 
