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 warm manure. 
For several days the worms living in this dry manure did 
not grow sensibly. Lack of direct warmth, but more espe- 
cially the want of sufficient 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 larger at. 
each stage. After feeding six or seven days 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 aboutto transform into the pupalstate, 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 days, asa 
winged being with legs and wings of which before there were 
no traces, and is animated by new instincts and mental 
traits. 
“Tf in its winged condition it is one of the most disagree- 
able features of dog-days and people wonder why flies were 
