ITS OUTER SKELETOX. 



53 



In Diptera both piercing and sucking parts are usually 

 present. The Gad-fly (fig. 25) is typical. Here we recognise 

 the labrum (Lbr), mandible (Mti), and maxilla (Mx l ) of the 

 Cockroach transformed into stylets. The maxillary palp (Mxp) 

 is still sensory. A pointed process, stiffened by chitinous ribs, 

 is developed from the back of the labrum. This is the 



LIBRA 



"Fig. 25. Mouth-parts of Gad-fly 

 (Tabanus). 



Fig. 25 A. Diagram of Mouth-parts 

 of Gad-fly. 



epipharynx (Ep), a process undeveloped in the Cockroach, 

 though conspicuous in some Coleoptera. All these parts are 

 overtopped by the suctorial labium (Lm), which has a two- 

 lobed expansion at the end. In the more specialised Diptera 

 this becomes a kind of cupping-glass. The Gad-fly is inter- 

 mediate between the Gnat, in which all the mouth-parts are 

 converted into piercing organs of extraordinary length and 

 sharpness, and such flies as the House-fly and Blow-fly, where 

 the sucking labium forms an organ of the most elaborate kind, 

 the piercing organs undergoing a marked reduction. Except 

 where the labium is short, it is doubly or trebly hinged, so that 

 it can be readily tucked away under the chin. 



