THE FLY 7 
INSECTA 
A DIPTEROUS INSECT. THE FLY 
Kill several bluebottle flies or large house flies, without injur- 
ing them, and impale one on a slender insect pin or a needle. 
Stick the pin or needle into a cork or a small piece of wood, 
in order to be able to handle it easily, and study the external 
anatomy of the fly with the aid of a hand lens. 
Observe the compact body of the animal, and note that it is 
distinctly divided, like that of the wasp, into three divisions — 
the head, the thorax, and the abdomen. Observe the color and the 
hairy surface of the body, including the legs and the wings. 
These numerous hairs are projections of the cuticula, and perform 
a useful function as tactile organs; that is, they are sensitive to 
vibrations of the atmosphere, and thus function as sense organs 
in that they aid in giving the animal a knowledge of its sui- 
roundings. Note the three pairs of long, strong legs and the 
single pair of wings. The fly has unusual locomotory powers. 
Correlated with these powers are the long cuticular hairs just 
mentioned, and also the very large composite eyes. An active, 
rapidly moving animal like the fly needs well-developed organs 
of orientation. The eyes are larger in the male than in the female, 
and are closer together on the top of the head. The two sexes 
may thus be distinguished. 
Between the large eyes are the three minute accessory eyes or 
ocelli. Note the peculiar form of the small antenna, with their 
pinnate terminal portion. Extend the proboscis and observe its 
complex structure and the oral lobes at the lower end. The fly 
eats only fluid food, which it sucks up through its proboscis. 
The thorax is of relatively large size, being almost entirely filled 
