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MOUTH-PARTS OF THE HORSE-FLY. 



{Tabanus or Therioplectes sp.; order Diptera.) 



Among the flies with piercing mouth-parts only the 

 females possess mandibles. It is therefore necessary to 

 select a female horse-fly (distinguished from the male by the 

 narrow space between the eyes ; in the males the eyes touch 

 each other for a greater or less distance along the dorsal 

 aspect of the head). 



The projecting mouth-parts are conspicuous. On super- 

 ficial examination there may be noted two, thickened, 

 slightly curving, horn or club-like processes (the maxillary 

 palpi) projecting above a black, thickened stalk or trunk 

 (the labium), on the dorsal surface of which lie several light 

 brown, slender, pointed stylets (mandibles, maxillae, labrum, 

 epipharynx, and hypopharynx). 



For the detailed examination of the mouth : parts, the head 

 of the fly should be removed from the body, a considerable 

 part of the head, laterad and caudad, broken away and the 

 remainder, with mouth-parts attached, boiled in KOH to 

 soften and bleach. 



The large maxillary palpi are two-segmented ; the distal 

 segment is longer than the basal one, and compressed. The 

 proximal one is subcylindrical, and projects dorso-cephalad, 

 so that the large distal segment is carried above the rest of 

 the mouth-parts. 



Lying along the dorsal surface of the large labial trunk 

 are six long, slender, pointed pieces or stylets. The upper- 

 most, unpaired, flat piece is the labrum (or perhaps labrum 

 and epipharynx fused). It is rather bluntly tipped and is 

 the broadest of the stylets. The flat, smooth, sharply 

 pointed mandibles lie just above the less strongly chitinized, 

 narrower, and finely marked maxilla. Corresponding some, 

 what to the labrum, but less broad and strong, is the sixth 



