ARACffiSTIDA AND INSECTA. 



175 



through a series of metamorphoses, presenting changes both 

 in their external form and in- 

 ternal structure, peculiar to 

 each successive stage; from 

 the egg is produced a vermi- 

 form animal, the larva; this, 

 after a time, becomes the chry- 

 salis, which finally develops 

 the perfect insect. The jaws of 

 insects (figs. 195 to 199) are 

 constructed after the type we 

 have already described in an- 

 nelida, Crustacea, and arach- 

 nida, that is to say, they are 

 placed laterally, and moved by 

 powerful muscles ; we recog- 

 nize two pair, an external pair, 

 or mandibulse (fig. 195, m\ 

 and an internal pair, or maxil- 

 Ise (j) ; the mouth is furnished 

 with a superior lip, or labrum, 

 and an inferior lip, or labium. 

 The development of the jaws 

 is in strict relation with the 

 natural food of the insect. The 

 suctorial apparatus of the hy- 

 menoptera, that of the common 

 bee (fig. 1 9G), for example, is 

 very singular; projecting from 

 between the jaws we observe a 

 sucker (/), composed of nume- 

 rous rings ; this organ, called 

 by Treviranus the fleshy 

 tongue, is situated at the com- 

 mencement of the esophagus, 

 in a horny sheath, formed by 

 a prolongation of the labise, 

 into which it can be with- 

 drawn at pleasure. The canal 

 of the sucker is very incon- 



Fig. 179. Digestive Organs of a 

 Beetle. 



a, the head which supports the 

 jaws ; b, the crop and gizzard ; d, 

 the chylific stomach ; c, the biliary 

 vessels ; d, the intestine ; e, secreting 

 organs ; /, the anus. 



