CHAPTEE VII 



DIPTERA OK FLIES ; APHANIPTERA OR FLEAS ; THYSANOPTEEA 



OR THKIPS 



Order VII. Diptera 



Wings two, ineriibranous, usually transixtrent and never very large ; 

 hehind the wings a pair of small erect capitate bodies — 

 halteres — frequently concealed under membranous hoods. 

 No distinct pirothorax, all the divisions of the thorax being 

 united, to form a large mass. Mouth-parts very variable, 



formed for suction not for biting, frequently assuming the 



form of a proboscis that can he retracted and concccded in a 

 cleft of the under side of the head. The metamorpihosis is 

 very great, the larvae bearing no resemblance whcttever to the 



perfect Insects, but being usually footless grubs or maggots ; 



frequently the head is indistinct, smcdl, and retracted. 

 Pupa variable, either exposed and rather hard, ivith the 

 appendages of the body more or less adherent ; or enclosed 

 in a scaly capside looldng like a seed, and vjhen extracted, 

 soft and delicate, with the appendages not fastened to the 

 body incapable of inovement. 



This definition of the Diptera, or two-winged flies, is framed 

 without reference to the fleas, which are wingless, or to a few 

 other parasitic wingless Diptera, such as the sheep-tick. Although 

 the Order is of enormous extent, these exceptional cases are 

 remarkably few. About 40,000 species of Diptera have been 

 discovered, but these are only a tithe of what are still unknown 

 to science. The Order is not a favourite one with entomologists, 

 and by the rest of the world it may be said to be detested. 

 Flies do not display the sort of intelligence we appreciate, 



