ORDER VII.—TWO0-WINGED INSECTS, OR FLIES. 303 
against the attacks of all insects, these flies will scent it a 
great distance, and, arriving at it in crowds, they deposit 
upon it their eggs, which are commonly called fly-blows. 
The maggots of this fly are well known in meat-shops, 
pantries, and kitchens, and are every where considered as 
disgusting in the extreme. They are spindle-formed, white, 
soft, and armed with two horny hooks, which enable them 
to move, and tear small pieces from the meat for their food. 
It is surprising how fast these maggots will develop. 
Signor Redi, a distinguished Italian naturalist, placed a 
fish at the disposal of these flies, upon which they soon de- 
posited their eggs. The second day after these maggots 
were hatched they doubled in size, when thirty of them 
weighed one grain; but from that moment they grew so 
fast, that on the next, or third day, one maggot alone 
weighed seven grains, thus becoming two hundred times 
heavier in twenty-four hours. These maggots arrive at 
their full growth in about four days, when they creep to 
the ground, change into an egg-shaped pupa, and come out 
as perfect flies a few days after. 
A great deal of instinct is exhibited by these flies in re- 
gard to the locality where they deposit their eggs, which 
must be a place that will furnish good food for their off- 
spring: forsinstance, if you set before them a thin piece of 
meat, however good, they will move over it and feed upon 
it, but will not deposit an egg upon it, because they know 
it will soon dry up; but if you put a piece of meat upon a 
damp or moist ground, where it will decay rapidly, it will 
soon be covered with eggs, the maggots of which will 
scratch it with their hooks, and soil it with their fluid 
evacuations, causing the whole piece to putrefy very rapidly 
and become fetid. 
The Meat-fly is a great lover of human cadavers, and 
in ancient times the people were much excited when it was 
ascertained that a human corpse was actually devoured by 
