14 THE MOUTH-ORGANS, ETC., OF 



daily constructed, something like oars, for propelling the insect 

 through the water. 



The mouth-organs of beetles, although all mandibulate and 

 constructed on the same plan, exhibit a great variety of forms in 

 their respective organs, according to the nature of the food on 

 which the insects subsist. Thus we find the carnivorous beetles 

 have mandibles very much hke the canine teeth of the tiger; 

 whereas those that feed on vegetables have their mandibles modi- 

 fied so as to act partly for cutting, but more particularly for crush- 

 ing, their food, like the molar teeth of the mammalia. At the 

 outset we are struck by the fact that all insects have mouth- 

 organs which work laterally, whereas all the vertebrata have the 

 motion of their parts vertically. 



The mouth-organs of a beetle consist essentially of six parts, 

 namely : the labrum, or upper lip j the labium, or lower lip ; and 

 between these there are two pairs of jaws, known as the ma?idibles 

 and the ?}iaxillce. The head which carries these organs is a box, 

 or perhaps more correctly a ring of chitine, articulated at its base 

 into the thorax, and open at the apex for the reception of the 

 various parts of the mouth. The front of this ring, or head, on 

 the upper side is called the Clypeus, on to which the labrum is 

 hinged like a flap \ it is usually square or oblong, but sometimes 

 rounded, slightly emarginate, or deeply cleft. On the under side 

 of the head there is, first, a plate, called the metitujn or chin, 

 generally straight at the base, rounded at the sides in front, and 

 deeply emarginate, sometimes with a projection or tooth in the 

 centre, which is often again notched ; attached to this is the 

 ligula, the representative of the lingua, or tongue. Beetles have 

 no true, free tongue, such as is possessed by the crickets. In 

 some — as the Dor Beetle, for instance — it is fleshy and partly free, 

 but in the Geodephaga it is attached to the labium, and forms, in 

 fact, its inner surface. To the base of the ligula is attached a 

 pair of palpi of four joints, and at its sides are a pair of pieces 

 called Paraglossia, but in a great many cases the Paraglossce are 

 cemented to the sides of the ligula, so that they are merged into 

 it ; they may be considered as a part of the tongue. These alto- 

 gether constitute the labium, or lower lip. 



Immediately under the labrum are the mandibles — a pair of 



