EXTERNAL ANATOMY OF INSECTS. 437 



chafer, in which at the base of one mandible is a con- 

 cave molary surface, and in the other a convex one, but 

 without any furrows : a circumstance that often distin- 

 guishes those that have furrows. — In the Dynastidce 

 the affinity of structure with the Melolonthida &c. 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 a . 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 

 perhaps 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 larvae that use their un- 

 guiform mandibles as instruments of motion b . Again : 

 amongst the Hymenopterous tribes, whose industry and 

 varied economy have so often amused and interested you, 



a One of these mandibles is represented in Plate XXVI. Fig. 

 20. a'", incisive teeth d'". molary plate. Comp. Linn. Trans, ubi 

 sapr. t. iii./. 4. c a b. b Vol. II. p. 275—. 



