SIPHONAPTERA AND DIPTERA 31 
The adults are practically wingless, though small, sealelike projec- 
tions from the top of the thorax show where the wings should be, and 
perhaps once were. The body is flattened laterally, thus enabling the 
insect to slip around easily among the hairs of its host. While the sur- 
face of the body is quite smooth and hard, it is provided with regular 
rows of stiff bristles, pointing backward, which help to force the insect 
in the direction in which it wishes to go, and likewise help it to escape 
from the fingers of its captor. A further evidence of its parasitic life 
is seen in the entire absence of compound eyes. The mouth parts are 
fitted for sucking. 
Diptera 
The insects falling within this order are easily recognized from the 
fact that they have only a single pair of membranous wings. The 
order includes the groups that we speak 
of as flics, mosquitoes, midges, and 
gnats. 
Metamorphosis is complete. The 
larva is commonly called a maggot, 
and is without feet. In most species 
it has no distinet head. In many sub- 
groups within this order the pupa or 
resting stage preceding the adult is 
peculiar in that it is inclosed within 
the hardened and shortened skin of 
the larva. 
The single pair of wings borne by 
the adult are on the middle segment 
of the thorax. On the hind segment 
Fra. 30. — Adult fly, Tabanus. 
Enlarged to twice natural size. 
ing the second pair of wings found in Original. 
are a pair of small knobs, represent- 
other insects. 
The mouth parts are primarily of the sucking type, but often are 
complex, and frequently are modified so that certain of the parts are 
fitted for piereing or for rasping. Thus, in the horseflies there are 
sharp lancets in addition to the sucking tube, the former penetrating 
