CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 17 



In one subdivision of the class Diplopoda, which is represented 

 by the genus Polyxenus and a few others, the mandibles are one- 

 jointed; and be- 

 mxt tween the mandi- 



»'^-l'> ' bles and the 



gnathochilarium 

 there is a pair of 

 one-jointed lobes, 

 which have not 

 been found in 

 other diplopods; 

 these are the "max- 

 illulas" (Fig. 21). 

 The correspondence 

 of the parts of the 

 gnathochilarium of 

 Polyxenus and its 

 allies with the parts 

 of the gnathocil- 

 larium of other di- 

 plopods has not 

 been satisfactorily 

 determined. 

 Most of our more common millipedes possess stink-glands, which 

 open by pores on a greater or less nimiber of the body segments. 

 These glands are the only means of defence possessed by millipedes, 

 except the hard cuticula protecting the body. 



The millipedes as a rule are harmless, living in damp places and 

 feeding on decaying vegetable matter; but there are a few species 

 that occasionally feed upon growing plants. 



For a more detailed account of the Diplopoda see Pocock ('11). 



Fig. 21. — The second pair of jaws, maxillulae, and the 

 third pair of jaws, maxillas or gnathochilarium, of 

 Polyxenus; the parts of the maxillae or gnathochila- 

 rium are stippled and some are omitted on the right 

 side of the figure: mh, basal membrane of the labium ; 

 la, "labium" of Carpenter, perhaps the mentum and 

 promentum of the gnathochilarium; mx, basal seg- 

 ment of the maxilla, perhaps the stipes of the 

 gnathochilarium; w:x;. /o, lobe of the maxilla; mx.p, 

 maxillary palpus; A, tongue or hypopharynx; mxl, 

 maxillula; fl. flagellate process (After Carpenter). 



