THE HEAD. 57 



teeth upon the inner margin of the maxillse, when present, are more 

 uniform, finer, and more delicate ; they are frequently, however, wholly 

 deficient,, and in lieu of them there are short bristles. In other instances 

 the whole superior process of the under jaw is clothed with short hair, 

 and such maxillae are called PENICILLATE (max. penicillatee, PI. IV. 

 f. 9) ; for example, in Lucanus. But this superior lobe presents itself 

 much more generally as a pergameneous, variously-shaped plate (max. 

 membranacece, PL IV. f. 2). They are SETOSE (max. setosce, s. setce 

 rostri infer lores) in the Hemiptera and many Diptera ; in some of the 

 latter (Tabanica) also LANCEOLATE (max. lanceolate?}. They are 

 UNGUICULATE (TO. tinguiculatfe), when the terminal tooth is moveable, 

 and can be moved to, and withdrawn from, the internal margin of the 

 superior lobe at the will of the insect (PL IV. f. 10). This superior 

 development of the lower jaw has hitherto been detected only in the 

 tiger beetles (Clcindelacea). 



We shall find the differences of the labium much more various than 

 any of the yet examined organs., probably by reason of its being more 

 compact than either of the others. 



We will first observe the chin, upon which we may almost repeat 

 what we said above of the labrum ; the differences of form are also 

 found in many other organs, and thus, as GENERAL, have been already 

 described in the first chapter. One peculiarity is its being more or less 

 deeply divided into two or three lobes, as well as its globose convexity 

 in the dragon-flies (Libellulhia, PL IV. f. 11 ). The tongue also has but 

 few exclusive peculiarities, and these we have already mentioned ; con- 

 sequently nothing further remains to be said upon it. The under-lip 

 of the larvae of the dragon-flies is of a very singular nature. The chin 

 is a thin stalk, which, in its pliable articulation, can be withdrawn 

 to the prothorax. Attached to it in front, and similarly articulated, 

 is the flattened, nearly longitudinal, heart-shaped tongue, which, in 

 repose, closes the orifice of the mouth, but which can also be distended 

 as a prehensile instrument. In front of the tongue there are two claws, 

 which, like the nippers of a pair of tongs, move in opposition to each 

 other, and thus capture objects between them. With these the larva 

 seizes its food, which consists of small water-insects, and then with- 

 draws its chin and tongue, so that its prey is brought directly in front 

 of the orifice of the mouth, when it very quietly sucks the insect dry. 

 The claws are analogous to the labial palpi. 



Much more various is the construction of the palpi. With respect 

 to the number of their joints they are subject to great variety ; but the 



