EXTERNAL ANATOMY OF INSECTS. 89 



the outlines occasionally given to illustrate genera, frequently 

 differed from my own dissections. Latreille, and several other 

 entomologists, have been fully aware of this discrepancy, which 

 is occasionally so great, that a figure, however accurate, of a 

 single mandible, will by no means characterise a genus. Every 

 description, therefore, taken from a single mandible, is faulty. 

 I am aware this will be found a sweeping censure ; but it ap- 

 pears to me nevertheless a sound one. The mandibles in all 

 these classes have denticulations or teeth more or less deve- 

 loped on their interior margins. It is to be observed, that the 

 mandibles are the maxillce by Linnaeus.? In Lejrkloptera 

 the mandibles are of a substance and size corresponding with 

 that of the upper lip.'i It does not appear that they perform 

 any office, or are possessed of any motion."^ In Diptera the 

 mandibles are elongate, pointed and lancet-like, and in most 

 respects, excepting the want of feelers, resemble the feeler-jaws. 

 They are now possessed of a decided motion, essentially diffe- 

 rent however from that of the mandibles of masticating insects. 

 Their motion is more of a vertical jerk, by which the insect 

 stabs them into the skin of the object which it attacks. The 

 precise character of the motion has not, however, been satis- 

 factorily ascertained. The variations of the mandibles in 

 Diptera are chiefly in size. In Hymenoptera the mandibles 

 are abbreviated, osseous, and masticatory. They now have a 

 distinct, free, and powerful horizontal motion, and, with the 

 feeler-jaws, close the mouth laterally. They are subject to 

 little variation throughout the class. In Coleoptera, the 

 mandibles are still more developed, forming by far the most 

 conspicuous part of the mouth. They do not so completely 



•" Lucanus scutellatus : maxillis exsertis apice bifurcatis latera unidentatis. — 

 Linnaius. 



^ Les mandibules sont d'une exiguete proportionee a celle de la l&vre supe- 

 rieure. Dans la plupart des especes elles paraissent k la loupe beaucoiip moins 

 grandes que les ecailles qui couvrent le chaperon : elles sont appuyees sur les 

 deux cotes de la trompe, et trop ecart^es pour pourvoir se toucher par leur 

 sommet. Leur mouvement est assez obscur et dans certains genres, comme 

 dans les Sphinx elles paroissent plutot soudees au chaperon qu'articulees ; 

 d'autrefois elles font corps avec la base de la levre superieure : elles sont 

 d'ailleurs cornees, tr^s lisses dessus et dessous, vides au dedans, tantot applaties, 

 tantot renflees, plus ou moins coniques; divergentes, parall^les ou convergentes; 

 pointues ou obtuses, suivant les genres, mais dans tous bordees de oils tr^s-fepais 

 sur leur tranchant intenevw:.— Savigny. 



' See Plate VL figs 1, 2, 3, 4, i. 

 NO. I. VOL. II, N 



