DIPTEEA. 



The term fly has come to signify a member of the order Diptera, tho in 

 combination the name is used in most of the orders, as sawfly, butterfly, 

 greenfly, whitefly, dragonfly, mayfly, etc. The most constant distinguishing 

 characteristic is the structure of the liind wing, which is a short slender 

 linobbed appendage called the halter, often covered and partly concealed by 

 a lobe of the front wing. When the front wings are absent the halters 

 also disappear. 



The mouth parts are extremely variable, sometimes all the parts are present 



Fig'ure 138 Wing of the house fly. 



but with mandibles and maxillae modified into piercing organs and the epi- 

 pharynx and hypopharynx may be developed into additional lancets, the 

 labium which is always without palpi forming a sheath enclosing all the lan- 

 cets. In the majority of flies the mouth is more or less simplified by the re- 

 duction or suppression of parts and in a few cases the whole mouth is rudi- 

 mentary. The labium remains relatively large in all functional mouths. The 

 one to five jointed maxillary palpi present the most characters of systematic 

 value in the varying number size and Shape of the joints 



The antennae show a great range of structure, being comparatively simple 

 and many jointed in the lower forms, but the higher flies have the third 

 joint enlarged and variously modified and the remaining joints reduced often 



129 



