THE COMMON HOUSE-FLY. 147 



On placing a fly in a glass bottle she laid, between 6 p. m. 

 Aug. 12, and 8 a. m. next morning, 120 eggs. They were 

 deposited irregularly in stacks, lying loose in two piles at 

 the bottom of the bottle. At 8 a. m. of Aug. 14, several 

 ^were found hatched and the maggots were crawling about. 

 The egg of the house-fly is long, cylindrical and a little 

 smaller at the anterior end than at the other. It is 0.4 to 

 0.5 of an inch long, and about one-quarter as thick. The 

 shell is very dense. The eggs hatch twenty-four hours after 

 being laid — in confinement they require five to ten hours 

 more, and the maggots hatched in confinement were smaller 

 than those reared from eggs deposited in v^rarm manure. 

 For several days the worms living in this dry manure did 

 not gro"w sensibly. Lack of direct w^armth, but more espe- 

 cially the v^ant of suflicient moisture and, consequently, of 

 available and semi-liquid food, seemed to cause them to be- 

 come dwarfed. It is evident that heat and moisture are re- 

 quired for the normal development of the fly, as they are for 

 nearly all insects. 



"The maggots moult twice, consequently there are three 

 stages of development, and they become sensibly larget- at 

 each stage. After feeding six or seven daj^s the larva is 

 nearly full grown; its body is long and slender, somewhat 

 conical, the head and mounth-parts being rudimentary; the 

 end of the body is truncated, and bears two short tubercles 

 or spiracles, which contain circular breathing holes with 

 sinuous openings, the edges of -which are armed with fine 

 projections, forming a rude sieve for the exclusion of dust 

 and dirt. When about to transform into the pupal state, the 

 body contracts into a barrel-shaped form, turns brown and 

 hard, forming a case, within which the larva transforms it- 

 self into a pupa. Our house-fly having, as a maggot, lived 

 a life of squalor, immersed in its revolting food, appears 

 after a short pupal sleep of from five to seven da3'^s, as a 

 winged being with legs and wings of which before there were 

 no traces, and is animated by new instincts and mental 

 traits. 



"If in its winged condition it is one of the most disagree- 

 able features of dog-days and people wonder why flies were 



