FEEDING AND BREATHING 21 



in small lumps. Very different is the form of the jaws of 

 insects that take their food in the liquid state. As an 

 example we may consider a blood-sucking fly (Fig. 7) such 

 as a breeze-fly (Tabanid). Here the median (unpaired) 

 organs of the mouth — the labrum-epipharynx, and hypo- 

 pharynx — are formidable dagger-like piercers (A, B) pro- 

 jecting downwards from the head. The mandibles (C) are 

 curved, with the base broad, the sharp edges tapering to a 

 fine point, like the blade of a broadsword ; by the action 

 of muscles these can be thrust out or pulled back. The 

 maxillae (D) are straight, narrower than the mandibles, with 

 their tips not only sharply pointed but armed with formid- 

 able barbs so that when thrust into the skin of the animal 

 whose blood is being sucked they hold firmly. Each 

 maxilla appears to be composed of lacinia and galea closely 

 united along their whole length. There is a short hairy 

 palp (Fig. 7, D,^) consisting of a single elongate segment 

 broad at the base and tapering to a point. The labium 

 (E) is a thick leathery organ with conspicuous bi-lobed 

 extremity along which run numerous channels strength- 

 ened by chitinous transverse rings, through which the 

 blood is draw^n into the hollow base of the labium, whose 

 cavity leads onward to the mouth and gullet. Other insects 

 that feed by suction may differ from the breeze-fly in the 

 form and arrangement of their jaws and other mouth parts. 

 Among bugs (Fig. 8) and their relations, such as " greenfly" 

 for example, the labium is modified into a stiff jointed 

 *' beak " (rostrum) with a groove extending along its front 

 aspect. Over the base of this groove lies the short, acute, 

 flexible lab rum, and within are found the mandibles and 

 maxillae, slender, strong piercers, the tips of the former 

 being barbed like those of the breeze-fly (Fig. 8, Mn, Ma). 

 These piercers can be thrust out beyond the extremity of 

 the beak, so as to puncture the tissues of a plant whence 

 sap can be sucked, or of an animal whence blood or other 

 nutritious fluid can be drawn. Such liquid food is sucked 

 in through the exceedingly fine tubular channel (Fig. 8, B, 5c) 

 formed by the concave inner surfaces of the piercers, and 



