MOUTH-PARTS OF INSECTS 295 



SECTION XIV. SPECIALIZED PIERCING MOUTH-PARTS 

 (TYPE, HORSE-FLY) 



Material. Specimens of any of the common horse-flies (Tabanus) will do 

 for this work, though only female flies can be used, as the mandibles are lack- 

 ing in the males. The two sexes may be distinguished by the position of the 

 eyes. In the male the eyes touch for a greater or less distance, while in the 

 female there is a narrow space between the eyes. The mouth-parts are quite 

 conspicuous and should be removed and mounted as in the previous section. 

 Students should also be provided with prepared slides. A comparison should 

 be made with the mouth-parts already studied. The mouth-parts of the fly are 

 more highly specialized than those of the squash-bug, and consist of a number 

 of stylets, or flat, pointed pieces, more or less completely inclosed in the fleshy 

 under lip. They consist of the following parts : 



1. Labrum. The labrum, or upper lip, is the uppermost stylet, 

 and consists of a flat, unpaired piece, bluntly tipped. It is broader 

 than any of the remaining stylets. 



2. Mandibles. These consist of a pair of flat, smooth, sharply 

 pointed pieces adapted for piercing. 



3. Maxillae. These are the second pair of stylets and are under- 

 neath the mandibles, which they very closely resemble. The max- 

 illae are narrower than the mandibles, are less strongly chitinized, 

 and are provided with palps, which are attached to the base of each 

 maxilla. The palps consist of two segments and are thick, clublike 

 structures covered with very fine hairs. 



4. Hypopharynx. The hypopharynx, or tongue, is a slender, 

 unpaired piece resembling very much the labrum, but is narrower 

 and more sharply pointed. It lies directly underneath the maxillae. 



5. Labium. This is a conspicuous, proboscislike structure, 

 which partially incloses the other mouth-parts. At the end of the 

 labium is a large, fleshy, disklike piece called the labella. It con- 

 sists of two lobes, which fit closely around the stylets when they 

 are being used. 



Exercise 41. Make careful drawings of the above mouth-parts. 



