THIRD EDITION 
The Pennsylvania State College 
Correspondence Courses in Nature Study 
OH 53 
. P5 
no. 1 
vopy 1 
imnt JUfe 
LESSON NO. I 
The House-Fly 
library of congress 
0 005 049 919 4' 
By George C. Butz 
T HERE is no insect that is more familiar to us, or more 
familiar with us, than the common house-fly; and yet 
few people know much about its life. It is well- 
named the housed y, for there is not a house all around the 
world in which it cannot be found during the summer. 
Houses that do not have fly-screens on the windows and 
doors are so badly infested with flies that the inmates suffer 
much annoyance. Pictures must be covered with screen- 
cloth and choice vases must be frequently cleaned. When 
we seek rest in the quiet perusal of a book, the naughty 
flies innocently alight upon our hands or faces, moist with 
perspiration, and torment us with the aggravating tickle of 
their peculiar mouth. Let us look at the fly closely to ob¬ 
serve its structure. 
The mouth is called a proboscis , and has a structure most 
peculiar. The proboscis of the elephant is his trunk, but it 
is the elongation of his nose. In insects the proboscis is a 
modified mouth, usually as a horny tube. In the fly it is 
bent up under the head when not in use. When the fly 
settles upon a sweet substance it unbends the tongue-like 
proboscis, and the knob-like end spreads out into two flat 
muscular leaves, with which the fly laps up sweet liquids, and 
so effectually teases us in the heat of summer. 
The eyes of the fly are no less remarkable. They are 
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