MOUTH OF INSECTS. 19 



34. The upper lip or labrum (la, fig. 4) is a flat piece fixed to 

 the anterior part of the head, and closes the mouth from above. 



35. The mandibles (m) are appendages, resembling large 

 teeth, which are inserted into the sides of the head immediately 

 below and behind the labrum; they are movable, and transverse, 

 that is, they are placed, one to the left and the other to the right ; 

 they are generally very hard and of a horny consistence. They 

 serve to divide the food. The mandibles of insects never have 

 palpi attached to them. 



35. The maxilla, or jaws (ma), are also two in number, and 

 are placed, one on the right and the other on the left, below and 

 behind the mandibles. Each jaw has, on its external side, a 

 little appendage formed of from four to six articulations, named 

 maxillary palpus (p) ; sometimes there are two palpi. In or- 

 thoptera the extremity of the palpus is often terminated by two 

 lobes ; in this case the external one is called the galea. 



37. The lower lip, or labium (li) closes the mouth from below, 

 and resembles a second pair of jaws, ordinarily joined on their 

 internal side, and in a great degree covered by a horny pro- 

 longation in the middle, termed the mentum, or chin ; the ligula 

 is another part of the labium. Each half of this lip supports a 

 palpus (pi, fig. 4) which is smaller than 



those of the maxillae, and consists of never 

 more than four articulations. 



38. The annexed figure (5) is a magni- 

 fied representation of the head of a cock- 

 roach (Blattd), seen from the front. A 

 careful examination of the figure will 

 more fully explain the several parts of the 

 mouth ; a, the antennae ; b, the com- 

 pound eyes; c, the ocelli or simple 

 eyes ; d, the labrum ; e, the mandi- 



bles; /, the maxillae or jaws; g, the Figt S. HEAD OF A 



ligula; h, the labial palpi ; i, maxil- ' COCKROACH. 



lary palpi. The principal use of the palpi 



is to seize and hold food between the mandibles, while it is being 



divided. 



Sometimes the jaws are enormously developed and form in 

 front of the head a sort of pincers ; an arrangement which is 



34. What is 7 the labrum ? Where is it attached ? 



35. What are mandibles in insects ? How are they placed in respect to 

 the labrum ? What is their number ? What is their use ? 



36. Where are the maxillae placed ? What is a maxillary palpus ? 

 What is meant by the galea 1 



37. What is the labium ? What is the mentum ? What is the ligula ? 



38. Of what use are the palpi ? 



