THE BITING MOUTH. 11 



dibles present every variety of form to suit them for 

 the almost infinite variety of offices to which they are 

 applied. 



Behind these horny jaws, which often attain most 

 formidable dimensions, and indeed can bite very 

 severely, we find a second pair of jaws, articulated, 

 like the first, to the sides of the mouth, but unlike 

 these composed of several horny pieces. Like the 

 mandibles also they are usually furnished with teeth 

 on the inside, and in many predaceous insects they 

 are curved and acute at the tip. To these jaws the 

 name of maxilla is given. On the outside each max- 

 illa is provided with a jointed organ, called & palpus, 

 which is inserted at the extremity of the third joint of 

 the maxilla. The palpi vary considerably in length, 

 and in the number and form of their joints; they 

 appear -to be employed as organs of touch. Within 

 them, in a few insects, there occurs a second palpus, 

 which however is very short, and never composed of 

 more than two joints; it is regarded as a modified 

 form of a portion of the body of the maxilla, which 

 only makes its appearance as a distinct part in a few 

 groups of insects. Jhe number of palpi, or jointed 

 organs attached to the maxillae (maxillary palpi as 

 they are called), is therefore either two or four. The 

 mouth is closed from beneath by the labium or lower 

 lip, which consists of two parts, namely the mentum, 

 or chin, a broad horny plate of very variable size and 

 form, and the ligula, or tongue, which lies upon the 

 inner surface of this, and is usually a membranous or 

 fleshy organ, although when it projects beyond the 

 mentum, it is generally supported by a horny plate. 

 The labium bears a pair of palpi (labial palpi) , which 

 are usually shorter, and composed of fewer joints than 



