32 ORTHORRHAPHA NEMATOCERA [CH. 



responsible for the transmission of the large number of parasitic 

 animals that occur in the blood of vertebrates, especially in 

 the tropics. Their great economic importance as carriers of 

 disease agents has become universally recognized during the 

 past twenty years and at the present time it is unnecessary 

 to dwell on this point. In fact there seems to be a tendency 

 for authors to go to the other extreme and credit biting 

 insects with the spread of almost every disease in which the 

 mode of infection remains unknown. Nevertheless, a large 

 number of species of biting-flies have been shewn to be respon- 

 sible for the spread of various diseases as may be seen from the 

 preceding table, in which are included all biting-flies that are 

 known to carry infections, together with the infection, or 

 infections, which they transmit (Table I). 



CHAPTER IV 



ORTHORRHAPHA NEMATOCERA 



Definition. As a rule a member of this series may be 

 easily recognized by its long thin body, slender legs and long 

 narrow wings. Moreover the antennae are long and filiform, 

 being composed of 6 to 15 segments that often bear whorls 

 of hairs, especially in the male. The larvae are aquatic, or 

 live in decaying organic matter {e.g. Phlehotomus) . 



The Nematocera includes some of the most important 

 biting-flies that carry disease, as the great family of mosquitoes 

 belongs to this group. 



Classification. Williston divides them into 12 families, of 

 which four are known to include members that either occasion- 

 ally or habitually feed on blood. In the present work his 

 method of classification has been adopted and the following 

 table includes all the families of the Nematocera. Those which 

 include any members that are known to carry disease are 

 printed in capital letters and will be discussed more fully. 



