2 Hewitt, Life-Jiistory of the Common House Fly. 



the Manchester weather on the rate of development. I 

 plotted out a curve of the daily mean temperatures 

 (taken from six readings) and found that a rise in 

 temperature produced an acceleration of the rate of 

 development at any stage of the life-history, that is, 

 shortened the time taken by that particular stage. 



In the larval state there are two moults, that is, 

 three stages can be recognised. In the first stage the 

 larvae have only one pair of respiratory apertures, or 

 stigmata, which are situated at the posterior end of the 

 body on the last abdominal segment. In the second and 

 third larval stages a pair of prothoracic or post-cephalic 

 stigmata are found in addition to the posterior stigmata. 

 The latter are slit-like in the second larval stage, two slits 

 to each of the stigmata. In the third larval stage they 

 are roughly semicircular with thickened chitinous rims 

 and the fiat sides opposite. 



The following table gives a summary of my results ; 

 the results of Packard and Howard are given at the 

 bottom for comparison. 



Series. 



Egg- 



Larva. 



Pupa. 



1 

 Total Time. 



1st stage. 



2nd stage. 



3rd stage. 



I 



24 hrs. 



3 days 



4 days 



6 days 



6 days 



20 days 



2 



24 hrs. 



2 days 



4 days 



4 days 



9 days 



20 days 



3 



36 hrs. 



2 \ days 



2 days 



6 days 



12 days 



24 days 



4 



24 hrs. 



2 days 



2 days 



7 days 



18 days 



30 days 



5 



24 hrs. 



2 days 



2 days 



8 days 



17 days 



30 days 



Packard 



24 hrs. 



1 day 



1 day 



3 or 4 days 



5-7 days 



io-i4days 



Howard 



8 hrs. 



1 day 



1 day 



3 days 



5 days 



10 days 



