THE PROBOSCIS: GLOSSINA 59 



evenly chitinized than in the Stomoxydinae. The labral apodemes 

 are correspondingly reduced, and are also thinner than those of the 

 forms so far dealt with. The buccal cavity is of the same type as that 

 of Mtisca, and consists of a small chamber, broader than long, and formed 

 from a single plate of chitin, the lateral edges of which are turned for- 

 wards and connected across the front by tough membrane ; the epi- 

 pharynx and hypopharynx terminate at this point in a manner similar to 

 that described for Musca. 



The haustellum appears on external examination to be an exaggeration 

 of the form seen in Stomoxys. It consists of two portions, the upper end 

 being swollen and bulbous, the distal part narrowed down to a fine 

 stylet ; the relative proportions of these being approximately one to two 

 and a half. When examined in sections and in cleared preparations it is 

 found that there are many important differences from the proboscis in the 

 Stomoxydinae. In the first place, the labella are not nearly so well marked 

 off from the labium proper, and are only very slightly thicker than the 

 adjacent part of the proboscis ; secondly, the labial gutter, and not the 

 mentum, is the main support of the proboscis. 



The labrum-epipharynx lies throughout in close contact with the labial 

 gutter, and since it does not, on that account, need to possess much 

 rigidity, it is a very delicate organ. The two constituent parts are close- 

 ly welded together, with only a small interval between them at the sides, 

 and together form a long inverted gutter; at the distal end, which is 

 situated just distal to the junction of the labium with the labella, the 

 gutter is very shallow, but further up the lateral portions are produced in 

 a circular direction, so that at the upper end the groove is converted to a 

 tunnel with only a small gap in its ventral wall. 



The external surfaces are in contact with the labial gutter, and are 

 provided with a row of short teeth which interlock with a corresponding 

 set on the gutter, the arrangement serving to prevent any displacement 

 of the organ from the groove in which it lies. The distal end is flattened 

 and soft, and is provided with a number of fine sensory hairs. At the 

 proximal end the two parts separate in the usual manner, the labrum be- 

 coming continuous with the membraneous anterior wall of the rostrum, 

 the epipharynx fusing with the anterior wall of the buccal cavity. 



The hypopharynx is an exceedingly delicate organ, composed of thin 

 and semi-membraneous chitin ; it does not assume the flattened form seen 

 in the other Diptera, and consists of little more than the wall of the sali- 

 vary duct, with some lateral membraneous expansions in the region of the 

 bulb. -For a considerable part of its extent, according to Stephens and 



