232 



3IYRI0P0DA. 



developed, lengthens somewhat, so that a stage resembling that 

 depicted in Fig. 118 is reached. 



The development of the limbs is the next point of importance. 

 It is as difficult here, as in the Chilopoda, to ascertain with certainty 

 the position of the antennae with relation to the mouth. The 

 antennae, as in Geophihis (Figs. 114 and 115), are specially highly 

 developed (Fig. 118, at). The mandibles also (mcl) are very large. 

 The rudiments of the maxillae are of special importance. According 

 to Metschnikoff's observations, which are conBrmed by v. Rath, 

 they arise out of a pair of limb-rudiments following the mandibles 

 (Fig. 116, uli), and are themselves immediately followed by the- 

 rudiments of the legs (p x —p 3 ). 



The Interpretation of the Mouth-parts of the Myriopoda. 



Whereas the Chilopoda have two pairs of maxillae and one pair of maxilli- 

 pedes, the Diplopoda possess only one pair of maxillae, which have united to- 

 form a lower lip, the gnathochilarium (Fig. 122, gch, p. 237), and possess no 

 maxillipedes. The structure of the adult gnathochilarium seems to indicate 

 that it has resulted from the fusion of two pairs of maxillae (Fig. 120, 



7nx z and mx 2 ), and this view 

 has repeatedly been adopted. 

 It is rendered all the more 

 probable by the fact that 

 the Chilopoda have two- 

 pairs of maxillae (Fig. 119). 

 These two would be homo- 

 logous with the first maxillae 

 and the lower lip of the 

 Insecta. Although such 

 an assumption seems both 

 likely and attractive, it 

 has not so far been sup- 

 ported by ontogeny, accord- 

 ing to which, as mentioned 

 above, the gnathochilarium 

 is derived from one pair 

 of limbs only (Metschni- 

 koff, No. 11, v. Rath, 

 No. 15). Further investi- 

 gation of these points is, 

 indeed, very desirable. The 

 structure of the adult mouth- 

 parts, however, seems to lead to a conclusion directly opposed to the above view 

 of the composition of the gnathochilarium out of two pairs of jaws. The 

 gnathochilarium of the Diplopoda (Fig. 120), like the first maxillae of the 

 Chilopoda (Fig. 119, stm + me + mi), is composed of several paired pieces, and 

 there is therefore a certain agreement between them. We may thus perhaps 

 conclude that the whole of the gnathochilarium is homologous with the first 



Fin. 118. — Embryo of Polydesmus comphmotus in a late 

 stage of development. The egg-envelope has been 

 removed (after Metschnikoff). at, antenna; ch, em- 

 bryonic cuticle ; d, yolk ; g, brain ; md, mandible ; 

 p t -p x , first three legs ; si, caudal lobe ; nk, maxilla. 



