62 MEDICAL ENTOMOLOGY 



The proboscis of Glossina is inserted into the skin for a considerable 

 depth, and the eversion of the teeth and upward displacement of 

 the external wall must be repeated with very great rapidity. Several 

 observers have noticed that when the fly commences to feed it produces 

 a faint humming sound, due to a rapid vibration of the wings ; this is 

 probably due to the extremely rapid respiratory movements by which the 

 blood is forced down into the labella, in order to reduce them to the 

 resting position in readiness for the next cutting act. 



The attitude of the fly while feeding is rather different to that of 

 the Stomoxydinae, for owing to the reduction of the amount of move- 

 ment possible between the rostrum and the head, and between the 

 rostrum and the haustellum, the fly has to raise itself a little on its hind 

 legs in order to adjust the tip of its proboscis to a position suitable 

 for feeding. 



Hippobosca and its allies present a curious condition, for while the 

 upper part of the proboscis, or rather the sucking apparatus simply, as 



it is never protruded from the head, resembles that 

 (Plat^XI fiif 3) ^ ^usca in many respects, the distal part or proboscis 



proper is more like that of Glossina. The Pupipara 

 are not descended from a Glossina-like form, but from some remote 

 ancestor common to it and to Musca. 



In the resting condition the whole of the sucking apparatus, corre- 

 sponding to the rostrum of Musca, and also the posterior part of the 

 haustellum, are concealed within the head. The distal part of the 

 haustellum, which, as in Glossina, forms a narrow piercing stylet, is 

 concealed between the palps, which alone are visible without dissection. 

 (Plate XIII, fig. 3.) When the mouth parts are required for use the ful- 

 crum is rotated in the same manner as in Musca, and by a similar 

 mechanism, with the result that the stylet is pushed forward between 

 the palps, and the pharynx, buccal cavity, and haustellum brought 

 into line with one another. 



The fulcrum and pharynx are of the same type as in Musca, but dif- 

 fer in detail. The ventral plate is strongly concave, and terminates 



posteriorly in very small outwardly directed cornua. 

 TIT b ^ e l a * era l P^tes are narrow, and converge towards 



one another in a V-shaped manner ; the anterior arch 

 is represented only by a short rod of thick chitin which lies between the 

 ends of the lateral plates and is directed antero-posteriorly. (Plate XIII, 

 fig. 6.) It is fitted into a semicircular notch at the distal end of the plate 

 of chitin which separates the eyes. The ventral wall of the pharynx 



