54 



EXTERNAL ANATOMY. 



FIG. 25.— Mandibles of Melan 

 oplus bivittntus; a, external view 

 b, internal view. Original. 



By removing the labrum, the 

 large, black-tipped, powerful, 

 toothed mandibles, {Fig. 25), are 

 seen, which meet each other on 

 the median line; their outer ends 

 articulate with the lower anter- 

 ior edge of the gena, by a joint 

 which allows them to move towards or away from the med- 

 ian line, but in no other direction. The large occipital fora- 

 men, b}'- which the cavity of the head communicates with 

 that of the neck, is bounded above by the epicranium, at the 

 sides by the gena, and below by a crescent-shaped sternal 

 plate, the gula. Movably articulated with the lower 

 straight edge of the gula is the labium or lower lip (Fig. 26), 

 formed by the union of a pair of appen- 

 dages, which are immovably united, but 

 still show upon the median lines traces of 

 this union. The labium consists of a basal 

 portion, the mentum [m); a pair of termi- 

 nal apron-shaped pieces, convex behind 

 and concave in front, the two halves of the ligula {li); on 

 each outer edge of the mentum is a small piece, the palpiger 

 [palpr), and upon this the three-jointed labial palpus {lb. p). 

 By removing the gula and the labium the posterior faces of 

 the anterior mouth-parts are exposed. Forming the poster- 

 ior boundary of the mouth, in the median line, is a dark- 

 colored chitinous spiny pad, the metastoma or tongue, 

 which has its anterior face covered with rows of spines. 

 Arching over the tongue and forming the anterior boundary 

 of the mouth are the black tips of the maxillae {mx), meet- 

 ing upon the median line. Each maxilla is 

 made up of a basal joint or cardo {co), which 

 is directed transversely to the long axis of 

 the head, and articulates with the lower 

 ixu^oi^M'Ti^no'. posterior edge of the gena. The second joint, 

 orrglna^'""*'"^" or stipcs {stip), runs forward at right 



FIG. 26. — Labium 

 or lower lip of Mel- 

 aaoplus bivittatus. 

 Original. 



