IN SECT A. 215 



lOD a. called lips; the upper one {fig. 100. a) the " la- 



'-~* brum," the lower one {d) the " labium:" but they 



have likewise four more complex jaws, acting upon 

 each other in pairs, from side to side, or trans- 

 versely to the axis of the body. The upper pair 

 of jaws (6) are called the " mandibles," the lower 

 pair (c) the " maxillse." The three lower instru- 

 ments, viz. the two maxillae and the labium, are 

 ^^^ ^ ^X) provided with the jointed instruments of sensation, 

 pSofi^ called " ^^alpi," the maxillee, in some insects, sup- 



TrophiofaMandibuiate Porting cach a pair of these appendages, which, 

 insect. besides their sensitive and selective offices, serve 



also to seize and hold steady the alimentary substances whilst these 

 are divided by the mandibles and maxillae. The lower lip has a 

 basal joint, or " mentum," supporting a more flexible part (ligula, or 

 labium proper), near to the base of which the palpi are articulated. 

 The upper, or inner integument of the ligula, is usually develojDed 

 into a kind of tongue, which is a distinct part (lingua') in the locusts 

 and Libellulae. The labrum, or upper lip, is generally a simple 

 transverse flattened plate. 



The mandibles are subject to most variety in relation to the habits 

 and kind of food of the insect. In texture they vary from the hardest 

 chitine to soft membrane. In the predatory tiger-beetles they ter- 

 minate in sharp hooked points, like canine teeth, and are hard enough 

 to pierce the firm integument of other insects. In the dragon-fly the 

 inner margin of the mandibles is armed with three or four sharp 

 laniariform processes. In some insects the upper dentations of the 

 mandibles have a trenchant edge, like incisive teeth ; while the lower 

 ones are broad and framed for bruising, like molar teeth, as in the 

 cock-chafler or the locust. The maxillae usually correspond with the 

 mandibles in their general characters ; but the teeth, which may be 

 developed from their inner edge, are more uniform and delicate : 

 their terminal piercing hook in the tiger-beetles is movable. The 

 maxillag are often clothed with short hairs. 



The mandibles of the bee-tribe are simple, but strong and trenchant ; 

 they are most important instruments in the economy of the different 

 species, and are modified accordingly. The maxillae and labium are 

 lengthened out to form the proboscis, but especially the lingual 

 process of the latter, which has two appendages, called " para- 

 glossae," developed from its base, and has its upper surface and sides 

 beset with hairs. 



In the Hemiptera both the mandibulae and maxillae are alike at- 

 tenuated, and prolonged into stiff neqdle or lancet-shajjed organs, 



p 4 



