LIFE-HISTORY 47 



spiracular processes of the larva. The fly levers itself out of the 

 barrel-shaped pupa and leaves the nymphal sheath" (Hewitt, 1908, 

 p. 510). By the successive inflation and deflation of the sac the 

 fly is able to make its way upwards through the manure pile, etc., 

 to the open air. Once liberated the wings, which have hitherto 

 been crumpled, expand, the integument hardens, and within an 

 hour or two the fly takes wing (see Figs. 8, 9). 



No further growth ever takes place after the wings have once 

 developed. 



The flies become sexuall}- mature in ten to fourteen days 

 after emergence from the pupal state, and four days after mating 

 they are able to deposit eggs. 



From these observations " it may be seen that in very hot 

 weather the progeny of a fly may be laying eggs in about three 

 weeks after the eggs from which they were hatched had been 

 deposited. As a single fly lays from 120 to 140 eggs at a time 

 and may deposit five or six batches of eggs during its life, it is 

 not difficult to account for the enormous swarms of flies that 

 occur in certain localities during the hot summer months, and 

 algebraical calculations are not required to more vividly impress 

 the fact" (Hewitt, 1908, p. 504). 



CHAPTER IV 



THE INTERNAL ANATOMY OF THE HOUSE-FLY 



The two most important contributions to the internal anatom^y 

 of non-biting muscid flies published in the English language 

 have been Lowne's (1895) monograph on the blow-fly and 

 Hewitt's (1907 — 10) papers on the house-fly. Both deal ver}- 

 thoroughly with the anatomy of the species under consideration, 

 and for detailed accounts of the various internal organs of these 

 insects the reader is referred to these works and to the various 

 papers dealing with special organs, which have been published 

 from time to time by other workers. In this chapter most of 



