DIPTERA. 419 



Cyclorrhapha with a frontal suture (Schizophora) 

 Normal Schizophora. 



The Thickhead-flies, Family CONOPID^E. p. 476. 



The Bot-flies, Family CESTRID/E. p. 477. 



The Muscids, Family Muscid.e. p. 479. 

 The Pupa-bearing Flies (Pupipara). 



The Louse-flies, Family Hippo roscidje. p. 487. 



The Bat-ticks, Family Nyctf.ribiid/E. p. 489. 



The Bee-louse, Family BRAULiDiE. p. 489. 



Classification of the Diptera. 



{For advanced students.) 



In the following table for determining the families of the Diptera 

 use is made chiefly of characters based on the form of the head, an- 

 tennae, and wings. 



The more important of the characters presented by the head are 

 the presence or absence of the frontal lunule, and the presence or ab- 

 sence of the frontal suture when the lunule is present. (See page 416, 

 note.) In those families that possess the frontal suture there exists 

 a large bladder-like organ, the ptilinum (ptil'i-num), which is pushed 

 out through this suture when the adult is about to emerge from the 

 puparium. In this way the head end of the puparium is forced off, 

 making a large opening through which the adult escapes ; afterwards 

 the ptilinum is withdrawn into the head. If a specimen is captured 

 soon after its emergence from the puparium, there may be seen in- 

 stead of the frontal suture the bladder-like ptilinum projecting from 

 the head, immediately above the antennae. 



The form of the antennae is of prime importance in determining 

 to what family a fly belongs. In the more generalized families the 

 antenna consists of many segments, which, except the basal two, are 

 similar in form (Fig. 487). Frequently such antennae bear whorls of 

 long hairs (Fig. 488). In the more specialized families there is a re- 

 duction in the number of segments of the antenna. This is brought 

 about either by a more or less complete consolidation of the segments 

 beyond the second into a single segment (Figs. 489 and 490), or by a 

 dwindling of the terminal segments, so that they form merely a slen- 

 der style (Fig. 491) or bristle (Fig. 492). Such a bristle is termed by 

 many writers the arista (a-ris'ta). In most cases where a stvle or 

 arista exists it is borne by the third segment, and this segment is then 

 usually greatly enlarged. When the enlargement of this segment has 

 taken place evenly the style or arista is terminal; but frequently one 

 part of the third segment is expanded so that it projects beyond the 



