414 



THE STUDY OF INSECTS. 



these rudimentary wings is not known ; but they doubtless 



have some important use, for they are present in nearly all 



flies, even when the front wings are wanting. 



The mouth-parts of flies are formed for sucking, and 



sometimes also for piercing. Their structure differs greatly 



in different families; and 

 in some cases it is exceed- 

 ingly difficult to determine 

 the correspondence of the 

 different parts. In the 

 more typical forms the 

 mouth-parts consist of six 

 bristle -like or lance -like 

 organs enclosed in a sheath, 

 and a pair of jointed palpi. 

 A difference of opinion 

 exists as to the corre- 



FlC. 482.-A crane-fly, showing wings and SpOlldeilCe of these parts ; 



halteres - but according to the most 



generally accepted view the six bristles represent the 

 upper lip (labrutti), the tongue (JiypopJiarynx), the two man- 

 dibles, and the two maxillae, and the sheath enclosing these 

 bristles is the lower lip {labium). The palpi which are not 

 enclosed in the sheath are the maxillary palpi. At the tip 

 of the lower lip there is, on each side, a lobe-like appendage ; 

 these are the labial palpi. The labial palpi of certain flies 

 are quite large ; in the House-fly, for example, they are ex- 

 panded into broad plates, which are fitted for rasping. 



In their transformations flies pass through a complete 

 metamorphosis. The larvae are commonly called maggots. 

 These are usually cylindrical and are footless; some possess 

 a distinct head, others do not; the form of the mouth-parts 

 varies greatly in the different families; and there are re- 

 markable variations in the form of the respiratory organs, 

 especially as to the number and position of the spiracles. 

 The pupse are usually either naked or enclosed in the last 



