24 CLASSIFICATION OF DIPTERA [CH. 



of which often carries an arista, usually terminal in position. 

 When an arista is not present the flagellum ends in an append- 

 age consisting of a number of indistinctly separated segments. 

 The maxillary palps are composed of one or two segments 

 and are not flexible. There is no definite arched suture above 

 the insertion of the antennae. The second longitudinal vein is 

 not forked, but frequently the third is forked ; the venation 

 is often very complex. This section includes the important 

 family of Tabanidae, in addition to a few other less well-known 

 forms. 



These first two divisions together constitute Brauer's sub- 

 order Orthorrhapha, which includes all those Diptera in which 

 the imago escapes from its pupal case by means of a dorsal 

 T-shaped opening or longitudinal slit ; accordingly ptilinum 

 and lunula are absent in the adult insect. The larva possesses 

 a distinct head and the pupa is usually obtectate. 



Series 3. Cyclorrhapha Aschiza. Flies without a frontal 

 suture and with a somewhat indefinite lunula. The antennae 

 are composed of not more than three segments of which the 

 end one bears an arista, which is not terminal, but usually 

 superior, in position. This group includes a large number of 

 very minute flies and also the great family Syrphidae, but none 

 of the members are known to suck blood and are therefore 

 of no interest in the present connection. 



Series 4. Cyclorrhapha Schizophora or Eumyiid flies. Flies 

 in which the antennae are composed of three segments and an 

 arista. None of the veins of the wing are forked. In the 

 Calyptratae the frontal suture is well-marked leaving a distinct 

 lunula over the insertion of the antennae. In the Acalyptratse, 

 the form of the head is less characteristic, but the members 

 of this section can generally be distinguished from the Bra- 

 chycera by their less complex wing venation. This group 

 includes the important family Muscidae, of which the common 

 house-fly, also Stomoxys, and Glossina are well-known examples. 



The latter two series together constitute the suborder 

 Cyclorrhapha, which may be defined as Diptera in which 

 the imago escapes from the pupal case by means of a circular 

 aperture at the anterior extremity produced by the pressure 



