MYRIAPODA. 



403 



more joints. In the Chilognatlia (fig. 253) are the Milli- 

 pedes and Galleyworms, characterised by their vegetarian 

 habits, by having the segments of the body so amalgamated 

 that the legs appear to be arranged in double pairs, and by 

 having antennae of six or seven joints. In the Pauropoda 

 is the single genus Pauropus, characterised by having only 

 nine pairs of legs, and the antennas bifid, with three long 

 multi-articulate appendages. Lastly, in the Onychophora we 

 have only the single and very anomalous genus Peripatus, 

 comprising worm-like Myriapods, with annulated bodies and 

 hooked or bristled feet. No member of the Chilopoda, Pauro- 

 poda, or Onychophora is known with certainty to occur in 

 the fossil condition, but various extinct types of the vege- 

 table-eating Chilognatha have been preserved to us, beginning 

 in the Carboniferous period. 



Fig. 253.-Millipede (lulus). 



The oldest-known Myriapods occur in the Coal-measures, 

 the two best-known genera being Xylobius and Archiulus. 

 These genera belong to 

 the order Chilognatha, and 

 comprise, therefore, vege- 

 table - feeders. In Xylo- 

 bius (fig. 254) the seg- 

 ments are divided by cross 

 sutures into numerous 

 fragments, in a manner 

 wholly unknown amongst 

 recent forms. Several 

 species of this genus are Fig 2 ^_ Xylobius SiglUariali a Cul , (onile rous 



known, Of Which the One Myriapod (after Dawson). a, Natural size ; 5, An- 

 terior portion, enlarged ; c, Posterior portion, en- 



figured above derives its 



specific name from the 



fact that it is found in the hollow trunks of Sigillaria. 



It must have possessed, like the living Galleyworms, the 



