DIPLOPODA. 



583 



bearing three pairs of legs, and a body consisting of numerous, for 

 the most part doubh segments. The gonad is ventral to the gut 

 and its ducts open on thz second or third post-cephalic segment. 



The body is, as a rule, cylindrical or sub-cylindrical (Fig. 356), 

 but sometimes it is flattened dorsoventrally. It frequently 

 possesses the power of rolling itself into a spiral or ball. In 

 many forms it is much elongated, but in the Oniscomorpha (and 

 Limacomorpha) the body is almost as broad as it is long. The 

 length varies from 2 mm. in Polyxenus to up- 

 wards of 200 mm. in some tropical Julidae 

 (Rhinocricus , Spirostreptus). The chitinous exo- 

 skeleton is hard (except in Pselaphognatha) 

 owing to the presence of calcareous salts, but 

 after moulting it is soft and usually paler. The 

 head (see p. 589) carries only three pairs of 

 appendages, the antennae, mandibles, and the 

 maxillae which are applied together to form a 

 gnathochilarium (or hypostoma). The antennae 

 are in general short and club-shaped, and con- 

 sist usually of seven segments, of which the 

 last is often concealed in the penultimate piece 

 and almost always bears four spines. The 

 eyes, which are aggregated and simple eyes, 

 are placed behind the antennae at the sides of 

 the head, more rarely on the middle of the 

 forehead. They may be completely absent, although the forms 

 in which this occurs do not differ in habits from those in which 

 they are present. They are usually numerous, but may be 

 reduced to 5, 3, or even 1 on each side. Between the eyes 

 and the antennae there is a small pit which may be provided 

 with a projecting hair. 



The labrum (upper lip) is continuous with the front of the 

 head (clypeus) and usually bears three teeth. The mandibles 

 (Fig. 347) are palpless, and consist of a stem (stipes mandibularis, 

 sti) and a distal portion (ma) which carries a powerful movable 

 tooth (de) and a plate with a broad masticatory surface provided 

 with toothed ridges (Ip). The gnathochilarium (Fig. 348) is 



der doppelfiissigen Myriopoden, Z.f.w.Z., 24, 1874. F. G. Heathcote, 

 The early development of Julus terrestris, Q.J.M.S., 25, 1883. Id., The 

 postembryonal development of Julus terrestris, Phil. Trans., 1888. 



FIG. 347. Right 

 mandible of Glo- 

 meris conspersx 

 (after Latzel). de 

 the large tooth ; 

 Id the toothed 

 plate ; Ip the 

 toothed ridjzes 

 (laminae pectin- 

 atae) ; ma distal 

 portion of the 

 stem (mala man- 

 dibularis) ; m 

 muscle ; sti stipes. 



