HABITS OF THE ADULT FLY 61 



posit their eggs; that is to say, from the fourteenth 

 day from the time of their emergence. The experi- 

 mental data upon which this statement is based are not 

 given in the paper in question, and the writer there- 

 fore wrote to him for a transcript of his record, from 

 which it appears that the flies under observation 

 emerged between August 2ist and August 28, 1907. 

 They were given fresh horse manure daily, and accu- 

 rate thermometrical readings were recorded for each 

 of the following days. Not until September 4th was 

 copulation observed, and on September Qth larvae were 

 found in the manure. 



Doctor Griffith, in his observations at Hove, found 

 that the female flies oviposited ten days after issuing 

 from the puparia, and that they could lay new batches 

 of eggs at intervals of from ten to fourteen days until 

 four batches have been laid. 



It seems to the writer that this period between issu- 

 ance and sexual maturity must surely be shorter, and 

 perhaps much shorter, under midsummer conditions and 

 in the freedom of the open air, than that indicated by 

 Hewitt and by Griffith. Breeding-cage observations 

 are never quite conclusive. 



So great is the practical importance of this point, 

 as already shown and as will be elaborated later, that 

 the most careful experimental work should be under- 

 taken under all sorts of circumstances and in very 

 many different localities. 



