370 ZOOLOGY 



infests cattle, squirrels, and other animals is Haematopinus, of 

 this there are several species. 



Order 7. DIPTERA (Flies). 



Chaeacteeistics. — Insects with piercing and sticking mouth 

 parts. The anterior u4ngs are memhranous ; the posterior 

 are replaced by knobbed processes — the halteres. The pro- 

 thorax is fused with the rest of the thorax. The meta- 

 morphosis is complete. 



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 Tipula, where they have thirty -six joints. 



The mouth parts consist of a soft sucking proboscis known 

 as the hatostdlum, 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 lialteres (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- 



