EXTERNAL ANATOMY OF INSECTS. 447 



As the principal use of the mandibles is cutting and 

 masticating, so that of the organs we are considering 

 seems to be primarily that of holding the food and pre- 

 venting it from falling while the former are employed 

 upon it. I say this is their primary use ; for I would by 

 no means deny that they assist occasionally in commi- 

 nuting or lacerating it. In fact, were there no organs 

 appropriated to this use, and if both mandibles and max- 

 illa were employed at the same time in comminuting the 

 food, it seems to me that it must fall from the mouth. 

 In a large proportion of insects the lobes of the maxilla 

 are not at all calculated for laceration or comminution ; 

 and in those tribes — as the Melolo?ithida> Rutelida, Dy- 

 nastidcB — in which they seem most fitted for that pur- 

 pose, the mandibles have incisive teeth at their apex, and 

 at their base a powerful mola or grinder : circumstances 

 which prove, that even in this case the business of mas- 

 tication principally devolves upon them. 



6. Palpi Maxillares a . There is one circumstance that 

 particularly distinguishes the maxilla from the mandi- 

 bles — they are palpigerous, as well as the under-lip. The 

 feelers, or palpi, emerge usually from a sinus observable 

 on the back of the maxilla where the upper lobe and 

 stalk meet. Their articulation does not materially differ 

 from that of the labial palpi. Each maxilla has properly 

 only one feeler ; but, as was lately observed b , in certain 

 tribes the upper lobe is jointed and palpiform, which 

 has occasioned it to be considered as a feeler, and these 

 tribes have been regarded as having six feelers. The 

 most general rule with regard to the length of the palpi 



a Plates VLVII. h". b See above, p. 443. 



