ANATOMY AND PHYSIOLOGY 



35 



The usual statement is that there are three pairs of mouth parts, 

 namely, mandibles, maxilla and labium. As a matter of fact, there are 

 four pairs, counting the superlingua, which are evident in Thysanura 

 and Collembola, become vestigial in Heterometabola, and disappear in 

 the most specialized Holometabola. The mandibulate, or primary 

 type (Fig. 45), from which the suctorial, or secondary type, has been 

 derived, will be considered first. 



Mandibulate Type. The labrum, or upper lip, in biting insects is a 

 simple plate, hinged to the clypeus and moving up and down; though 

 capable of protrusion and retraction to some extent. It covers the man- 



FIG. 45. Mouth parts of a cockroach, Parcoblatta pennsylvanica. A, labrum; B, 

 mandible; C, hypopharynx; D, maxilla; E, labium; c, cardo; g (of maxilla), galea; g (of 

 labium), glossa; I, lacinia; Ip, labial palpus; m, mentum; mp, maxillary palpus; p, paraglossa; 

 pf, palpifer; pg, palpiger; s, stipes; sm, submentum. B, D, and E are in ventral aspect. 



dibles in front and pulls food back to these organs. On the roof of the 

 pharynx, under the labrum and clypeus, is the epipharynx; this consists 

 of teeth, tubercles or bristles, which serve in some insects merely to hold 

 food, though as a rule the epipharynx in mandibulate insects bears end- 

 organs of taste (Packard). The labrum does not represent a pair of 

 primary appendages. 



The mandibles, or jaws proper, move in a transverse plane, being 

 closed by a pair of strong adductor muscles and opened by a pair of 

 weaker abductors. The mandible is almost always a single solid piece. 

 In herbivorous insects (Fig. 46, A) it is compact, bluntly toothed, and 



