BEETLES. 303 



an extraordinary size, and are sometimes branched. Beneath the mandibles are the 

 maxillae, which are more delicate and more complex than the mandibles, and which 

 aid the latter in masticating, apparently performing the lighter and more complicated 

 part of the work. The basal articulation of each maxilla is termed the cardo, to this 

 is attached the stipes, with an external scale-like segment, the squama palpigera; to 

 the squama palpigera a multiarticulate palpus, the palpus maxillaris, or maxillary 

 palpus, is jointed. Two lamellar lobes, the real chewing-organs of the maxillae, are 

 also attached to the upper edge of the stipes ; these are termed, respectively, the lobus 

 externus, and the lobus internus. In the Cicindelidae, Carabidse, and DytiscidEe, the 

 lobus externus is palpiform and usually two-jointed. The maxillary palpi generally 

 have four joints. Beneath or behind the maxillae is, homologically, a thii-d pair of 

 buccal organs, a second pair of maxillae, the two halves of which are united together 

 at their bases, which latter are also united above with the ligula or tongue, and below 

 form the mentum or chin. The ligula and mentum, the last of which articulates with 

 the lower portion of the head by the gular suture, are important in the classification 

 of Coleoptera. Joined to each side of the ligula is a palpus labialis, usually three- 

 jointed. A membranous process usually exists on each side of the ligula near its tip ; 

 these j)i*ocesses are the paraglossae. 



The labriim above and the labium beneath, in Coleoptera, as in other chewing 

 insects, are passive in function, serving to hold the food in place while it is masticated 

 by the mandibles and maxillae. As the cheeks in higher vertebrates prevent a side- 

 wise or lateral squeezing out of the food from between the teeth, so the labrum and 

 labium of Coleoptera keeps the food in its position between masticatory organs which 

 operate laterally. All the mouth-parts of adult Coleoptera are subject to slight modi- 

 fications and reductions in certain families and genera, and in the larvae the oral organs 

 are not rarely considerably modified. The larvae of Dytiscidae and Hydrophilidae pre- 

 sent remarkable modifications of form and use, which, as in the case of other striking 

 variations from the normal form of larval mouth-parts, will be described under their 

 respective families. 



The prothorax, the middle of the three portions into which all beetles are divided 

 with considerable distinctness, is hollowed out in front to receive the neck or head, 

 and is articulated behind with the mesothorax. The prothorax bears the forward 

 legs. Its dorsal surface is often termed the pronotum. 



The mesothorax, metathorax, and abdomen form the last of the three portions of a 

 beetle, which portion is often called the trunk. 



The mesothorax and metathorax are very intimately united ; upon the former are 

 borne the elytra and middle pair of legs, and upon the latter the wings and hijid pair 

 of legs. Both mesothorax and metathorax are hidden from view, on the dorsal side 

 of the insect, by the elytra, except that in most beetles a small triangular portion of 

 the mesothorax is visible between the elytra at their bases ; this triangle is the scu- 

 tellvim. The median ventral pieces of the three different parts of the thorax are 

 termed, respectively, presternum, mesosternum, and metasternum, and the pieces 

 which connect each of these sternal pieces at the sides with the dorsal pieces, are 

 termed the epistema and epimera, respectively, of the prothorax, of the mesothorax, 

 and of the metathorax. The sutures between certain of the above-mentioned parts 

 may be obliterated in some cases. 



The abdomen is broad anteriorly, is closely united with the metathorax, is in most 

 cases entirely covered or protected from above by the elytra, and contains the sexual 



