CHAPTER VIII 

 TWO-WINGED FLIES AND FLEAS 



NEARLY all winged insects are known popularly 

 as " flies," but the name is most fittingly 

 applied to members of the sixteenth order, or Diptera. 

 These are the " true flies," or " two-winged flies," 

 which differ from all other insects in having the hind- 

 wings reduced to tiny stalked knobs, or halteres (p. 7), 

 the fore-wings alone being used for flight. These 

 functional wings are usually transparent, with not 

 more than seven longitudinal nervures. The com- 

 pound eyes are generally large and conspicuous. 

 When present, the mouth-parts are greatly modified 

 so as to serve for piercing and sucking, or for sucking 

 only. The common grey gnat, or mosquito, for 

 example, has no less than six needle-like stabbing 

 instruments, that are believed, with good reason, to 

 represent the mandibles, first maxillae, labrum, and 

 " tongue" of a typical mandibulate insect, such as the 

 cockroach. All the six needles lie normally within a 

 grooved sheath (the modified second maxillae, or 

 labium) ; but when a gnat " bites," the needles are 

 driven through the skin of the victim, while the 

 sheath loops back under the insect's head. The 

 extreme tip of the sheath, however, remains closely 

 pressed to the skin, and surrounds the needles. The 

 actual sucking-tube, through which blood is drawn 



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