370 ZOOLOGY 
infests cattle, squirrels, and other animals is Haematopinus, of 
this there are several species. 
OrvER 7. DIPTERA (Flies). 
CHARACTERISTICS.—Jnsects with piercing and sucking mouth 
parts, The anterior wings are membranous ; the posterior 
are replaced by knobbed processes—the halteres. The pro- 
thorax is fused with the rest of the thorax. The meta- 
morphosis 7s conyplete. 
The Diptera form one of the largest orders of insects, and 
when completely worked out it will probably be found to 
include at least as many species as the Coleoptera. The mem- 
bers of the order are of moderate size, with freely moveable 
spherical heads. The compound eyes are large, and in the male 
they sometimes fuse together across the dorsal middle line. 
There are three ocelli. The antennae are either short and end 
in a tactile hair—the arista,—as in Musca, or are long and fili- 
form as in Zipula, where they have thirty-six joints. 
The mouth parts consist of a soft sucking proboscis known 
as the haustellum, ending in two swollen lobes. This is partly 
formed by the labium, which is devoid of palps. In front of 
this lies the elongated labrum, and between the labrum and 
labium an unpaired stylet, the epipharynx. The mandibles 
and first maxillae also form stylets, and the latter are provided 
with palps. Both the mandibles and maxillae may be rudi- 
mentary. 
The mesothorax forms the largest part of the thorax. 
The wings are transparent, with few nervures, and with micro- 
scopic hairs and scales. The inner margin of the wing is 
usually notched, dividing it into two lobes, the alula and 
squama. They vibrate with great rapidity, 350 times per 
second in the fly. In a few cases they are absent. 
The posterior wings are replaced by halteres (Fig. 209), 
which are short processes usually ending in a knob, Their 
function is not definitely determined, but to some extent they 
appear to act as balancers, and when removed the fly cannot 
control its flight. 
The legs are slender and often long; the tarsus is five- 
