INTERPRETATION OF THE MOUTH-PARTS OF THE MYRIOPODA. 



233 



pair of maxillae of the Chilopoda. Another pair of limbs will then have been 

 drawn into the formation of the mouth-parts in these forms, and will have 

 yielded the second maxillae. That such an inclusion of a pair of legs among 

 the mouth-parts is not inadmissible in the Myriopoda is shown by the change of 

 the first pair of legs in the Chilopoda into maxillipedes. The second maxillae 

 of the Chilopoda themselves do not essentially differ from legs (Fig. 119, pi), 

 and the fact that, in the Diplopoda, the first pair of legs may shift to a position 

 very near the head (Fig. 122, b, p. 237), does not seem without significance. 



According to this last view, a comparison of the mouth-parts of the Myriopoda 

 with those of the Insecta would suggest that the gnathochilarium of the 

 Diplopoda and the first maxilla of the Chilopoda should be homologised only 

 with the first maxilla of the Insecta. The second maxilla of the Chilopoda 

 and the first pair of legs of the Diplopoda, on the other hand, would correspond 

 to the lower lip of the Insecta. The external similarity of the plate-like 

 gnathochilarium to the lower lip of many Insects would be explicable not 

 through a direct homology between the two structures, but merely through 

 the similarity of their functions. 



The mouth-parts are fully developed even during embryonic life, 

 and therefore have attained their definite form when the young 

 animal hatches (v. Eath, Fig. 122). Three pairs of legs are at first 

 developed in the larva (Fig. 121 B), but these do not always appear 

 to belong to three consecutive segments. Thus, in the larvae of 

 Sirongylosoma and Poly- 

 desm/us (Figs. 121 B, and 

 122), the segment coming 

 next but one after the 

 head carries no limbs ; 

 in the larva of Jul us, 

 this is the case with the 

 third segment (Xewport), 

 in keeping with the 

 absence of limbs on that 

 segment in the adult. 

 The third pair of legs 

 is followed by the rudi- 

 ments of several other 

 limbs, which, however, 

 vary in number in the 

 different forms. These 

 limbs are at first truncated 

 and are hidden under the integument, only appearing as free legs 

 during post-embryonic life. The number of segments has increased 

 posteriorly, so that when hatched, the larva usually has from seven 

 to nine trunk-segments, but the number of these also seems to vary 



Fig. 119. — The head of Lithdbius validus, seen from 

 below (after Latzel, from Lang's Text-book of Comp. 

 Anat.). a, antenna ; me, outer, mi, inner blade of 

 the first pair of maxillae ; pi, palp of the second pair 

 of maxillae ; oc, ocelli ; sk, ventral portion of the 

 cephalic shield ; M, basal plates of the second 

 maxillae ; stm, basal plates of the first maxilla. 



