12 DURHAM DIPTERA. 



(B.I.) (3) At the back of the alar regions is a ridge, the alar 

 frenum (12), separated by a hollow from the 

 scutellar bridge (11). The scutellar bridge and 

 alar frenum = the postalar calli. 



(4) Bristles. — The larger bristles or macrochcetce are 



distinguished by the names of the regions. The 

 arrangement of bristles is termed choztotaxy. 



(5) The Dorso- Central Priz- or Post-sutural Bristles, 



inner (13) or outer (14) rows, are on the prae- 

 sutural and post-sutural central regions. When 

 they are all absent, except one or two behind, 

 then these latter are often called the pr<z- scutellar 

 bristles. Acrostichal bristles, rows of minute 

 bristles on the centre of the dorsum. 



(6) The Humeral Bristles, on the humerus. 



(7) The Post-humeral Bristles, behind the humerus on 



the edge of the dorso-pleural suture. 



(8) The Intra-humeral Bristle, near the upper border 



of the post-humeral region. The proz-sutural 

 bristle, near the inner hind corner of the post- 

 humeral region. 



(9) The Supra-alar Bristles, generally three, two on 



the edge of the alar frenum, and one in front, 

 forming a kind of triangle above and rather 

 behind the root of the wing. 



(10) The Intra-alar Bristles, on the fore part of the alar 

 region. 

 II. The Sides, or Pleura. 



III. The Breast, or Sternum. For practical purposes, 

 the pleura and the portion of the sternum seen in 

 a side view, are considered together. 

 Divisions : — 



(1) The Prothorax, below the shoulders and above the 

 fore-leg. Behind it is bounded by the pro- 

 thoracic suture, a seam coming down from the 

 dorso-pleural suture, in front of the hairy 



