248 PTILOTA: IMAGO EXTERNAL ANATOMY. 



bulated insects must, of course, be characterized by the hori- 

 zontal motion of their jaws, and not, as might, perhaps, from 

 the names of the two groups, be supposed, upon the presence 

 of mandibles in the Mandibulata, or their absence in the 

 Haustellata; because, as I have already said, the mandibles 

 or their representatives are to be found in all insects. It 

 would, indeed, perhaps be advisable to adopt other terms 

 in lieu of these, but as they are generally understood, I 

 shall continue to speak of the mandibulated and h:uistcll:itcd 

 insects, in alluding to the species distinguished by the biting 

 or sucking mode in which they take their food. 



Moreover, instead of treating of these two groups separate- 

 ly, as has been generally done, it will perhaps be more advan- 

 tageous, as enabling us more readily to show the modifica- 

 tions which each organ undergoes, to take the various or- 

 gans seriatim prefacing their description by the following 

 general observations. 



In biting insects, or those which feed upon solid matters, 

 the four lateral pieces perform the office of jaws, and move 

 in a horizontal direction, the two other pieces being regard- 

 ed as lips ; the upper jaws are more particularly denomi- 

 nated mandibles; and the lower jaws are named maxillee, 

 and, in general, each of the latter is furnished with a slendrr- 

 jointed appendage termed a palpus, which is never found 

 attached to the mandibles of winged insects ; in some of the 

 wingless insects the mandibles are, however, also palpL'emus. 

 The maxilla are generally terminate*] by two lobes, the outer 

 one being very variable in form. The upper lip is termed 

 tlie Itibrum, and the lower lip labium; but the latter is a 

 much more complicated instrument than the former, and is 

 furnished, like the tnaxilUe, with two short articulated 

 palpi. 



In the sucking insects, the nutriment being essentially 



