12 BULLETIN 345, TJ. S. DEPARTMENT OP AGRICULTURE. 



or observations in support of his statement that the fly repeats the 

 process of egg laving 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 after 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., a few lived as long as 70 days. This record was not included 

 in calculating the mean longevity. 



