10 DURHAM DIPTBRA. 



(A. IV.) (6) The Arista or Seta. — A bristle or spine springing 

 from the third joint, either at some point of the 

 upper surface between the base and the point, 

 when it is said to be dorsal — it is generally 

 jointed and often bears hairs, when it is said to be 

 plumed or plumose if the hairs are very long, 

 combed if they are only on one side, hairy if the 

 hairs are rather short, pubescent if they are very 

 short, and bare if they are absent — or if the bristle 

 or spine springs from the extreme point of the 

 third joint it is a terminal arista (Plate III. 29), 

 and if very strong it is called a style (Plate III. 22). 



V. The Face. — The part above the mouth and below 

 the antennae. 



(1) The Facialium. — A ridge bounding the face on each 



side. 



(2) The Facial Bristles. — A row of bristles on the 



facialia. 



(3) The Mystax. — Strong hairs on the front of the face 



and overhanging the mouth (Plate VI. 28.b). 

 VI. The Cheeks or Gen^e. — The spaces at the sides of 

 the face, between the facialia and the eyes. They 

 are sometimes divided into two parts by a ridge or 

 seam, when the part nearer the eye is called the 

 genal orbit or eye-margin (Plate VII. 5). 



VII. The Jowls. — The parts below the cheeks and the 



eyes. 



VIII. The Mouth. 



(1) The Peristome or Mouth Edges. — The part im- 



mediately surrounding the mouth. The epistome 

 is the part above the mouth, or the upper edge. 



(2) The Mouth Bristles or Vibrissce. — One or more 



strong bristles close to the sides of the mouth. 



(3) The Proboscis. — The jointed sucking instrument, 



sometimes withdrawn within the mouth-cavity, 

 sometimes long and protruding. 



