1(54 PHYSIOLOGY OF INSECTS. 



tally. Rudimental mandibles or mandibulae incipientes, 

 are those which are perfectly without motion and appa- 

 rently without use ; they are small, scale-like processes 

 adhering to the skull, and are utterly incapable of gnawing 

 solid substances : they have this form in butterflies. Li- 

 near mandibles or mandibulcB lineares, are those which 

 are of uniform size and substance ; which are perfectly 

 straight, parallel, and approximate ; they are always with- 

 out the horizontal motion, and utterly incapable of gnawing 

 solid substances : they have this form in many flies. Tu- 

 bulate mandibles or mandibulae tubulates, are those which 

 are hollow, and perforated at the extremity to admit the 

 passage of the blood of other insects, on which the insects 

 possessing such mandibles always feed: the mandibles 

 possess this form in the larvae of some carnivorous beetles, 

 and in that of the ant-lion. Falciform mandibles or man- 

 dibulce falciformes, are when they are long and much 

 curved, in the shape of a sickle ; they move horizontally 

 with great ease, are hard and acute, and, when closed, 

 cross each other : insects possessing these mandibles bite 

 severely, and prey on other insects. Bifid mandibles or 

 mandibulce bifidce, are when the extremity is terminated 

 by two distinct points of equal length and similar ap- 

 pearance, otherwise one of them would be called a tooth. 

 Toothed mandibles or mandibulae dentatae, 

 are when the internal mandibles are beset 

 with teeth : when this is the case, they are 

 hard and bony, have a rapid and powerful 

 Mandible. horizontal motion, and are capable of grind- 

 ing very hard substances. Setiform mandibles or mandi- 

 bulte setiformes, are when they are very slender, flexible, 

 thread-like, without horizontal motion, and often com- 

 pletely enclosed in a sheath, which sheath is generally 

 supposed to be the lower lip. 



