436 EXTERNAL ANATOMY OF INSECTS. 
affinity of structure with the Melolonthide &Xc. is more 
pronounced, the furrows to which ridges in the other 
mandible correspond being reduced to one or two wide 
and deep ones; whereas in some of the latter tribe they 
are very numerous. ‘These mandibles, in many cases, 
at their apex are furnished with incisive teeth to cut off 
their food, and with miniature mill-stones to grind it *. 
The part here alluded to I call the Mola. 
Were I to ask you what your idea is with regard to 
the use of the organs we are considering, you would per- 
haps reply without hesitation, ‘ Of what possible use 
can the jaws of insects be but to masticate their food ?” 
But in this you would in many instances be much mis- 
taken ; as you will own directly if you only look at the 
mandibles of the stag-beetle—these protended and for- 
midable weapons, as well as those of several other bee- 
tles, cannot be thus employed. ‘ Of what other use, 
then, can they be ?” you will say. In the particular in- 
stance here named, their use, independent of mastica- 
tion, has not been satisfactorily ascertained; but in many 
other cases it has. Recollect, for instance, what I told 
you in a former letter, of those larvee that use their un- 
guiform mandibles as instruments of motion. Again: 
amongst the Hymenopterous tribes, whose industry and 
varied economy have so often amused and interested you, 
many have no other tools to aid thein in their various 
Jabours and mechanical arts: to some they supply the 
place of trowels, spades, and pick-axes; to others that 
of saws, scissors, and knives—with many other uses that 
* One of these mandibles is represented in Plate XXVI. Fic. 
20. incisive teeth a”. molary plated”. Comp. Linn. Trans. ubi 
supr. ¢. iii. fi 4. ca 6. Vo. II. p. 272—. 
