418 



ZOOLOGY. 



\ 



mandibles, they serve chiefly to cut the materials with which 

 the hymenoptera make their nest, or to seize and put to 

 death the prey of which these insects suck the juices: It 

 has been remarked also, that there exist in the interior of 



the mouth other solid pieces 

 which are absent in the 

 grinding insects, and which 

 constitute valvules intended 

 to close the pharynx every 

 time that deglutition does 

 not take place. 



523. In the wood- 

 bug, the chirping grass- 

 hopper, the vine-fretter, and 

 other hemipterous insects, 

 the apparatus of suction is 

 composed of the same ele- 

 ments, but a little diffe- 

 rently arranged. The mouth 

 is armed with a tubular 

 and cylindrical bill or beak, 

 directed downwards and 

 backwards (Fig. 438), and 

 composed of a sheath en- 

 closing four stylets ; the 

 sheath (a, Fig. 439) is in its 

 turn formed of four joints, 

 placed end to end, and re- 

 presents the lower lip; 

 finally, the stylets (b c), 

 which have the form of 

 slender filaments, stiff and 

 serrated at their summit, 

 to enable them to pierce the 

 skin of animals or the tissues 

 of plants, are the represen- 

 Fig. 440.-Nemestrina longirostris. tatives of the mandibles and 



jaws, extremely elongated. 



In the hemiptera, which live at the expense of animals, the bill 

 is in general very strong, and folded into a semicircle under 

 the head. In those which are nourished on the juices of 

 vegetables, it is, on the contrary, almost always slender, and 

 applied in repose against the inferior surface of the thorax 



