584 



CLASS III. MYRIAPODA. 



FIG. 348. Gnathochilarium, A of Glomeris, 

 B of Jidus (after Latzel). i Hypostoma 

 (basilare) ; a mentum (infrabasilare) ; 

 6 promentuni : d lingua ; g lolii linguales : 

 h cardo gnathochilarii ; c stipites gnatho- 

 chilarii ; e mala gnathochilarii exterior ; 

 / mala gnathochilarii interior. 



formed by the junction of the second pair of mouth parts (maxillae) 

 which in early life are distinct. It strongly recalls the labium 

 of insects, with which however it can hardly be homologous, 



(see table of comparison p. 

 325). It consists of a more 

 or less flat plate which forms 

 a lower lip and shows a number 

 of different parts marked off 

 from one another more or less 

 perfectly by thin seams in the 

 chitin. Except in the 

 Polyxenidae and Polyzonidae, 

 in which the gnathochilarium 

 is degenerate, the parts shown 

 in Fig. 348 may be made out. 

 Of the post-cephalic segments, 

 two are specially varied in 

 form, viz., the collum or neck 

 segment, which comes next behind the head, and the anal 

 segment. The collum varies much in the size and shape of 

 its tergal plate. In the Platydesmidae it is larger than the 

 head, in Polyzonidae it 

 is semielliptical, in Psela- 

 phognatha it is small 

 and narrow, in Chor- 

 deumidae it is elliptical 

 and convex, and in the 

 Polydesmidae it is of 

 every variety of shape 

 and size. The anal seg- 

 ment is larger than the 

 others and in many 

 species its tergum is pro- 

 longed into a spike which 

 serves as a specific char- 

 acter. 



The first four segments (Fig. 349) which may be regarded 

 as a kind of thorax, carry only three pairs of appendages 

 amongst them, one being apodal. From the fifth segment 

 (in the Polyzonidae from the fourth) each segment carries 



FIG. 349. Ventral view of head, thorax, and first 

 double segment of a female Polydesmm com- 

 planatus (after Latzel). Goe female generative 

 opening ; D alimentary canal. 



