3o8 



PHYLUM ARTHROPODA. 



out. The nervous system, the tracheae, the heart, the ex- 

 cretory tubules, etc., are like those of Insects. It cannot 

 be said that the centipedes (Chilopoda) and the millipedes 

 (Diplopoda) are very closely related to one another, and 

 there are two other distinct orders, Symphyla and Pauropoda. 

 The resemblances are in part resemblances of convergence, 

 not of genuine affinity. Simple wingless insects, known as 

 Collembola and Thysanura, are closely approached by such 

 Myriopods as Scolopendrella ; and it is likely that Myriopods 

 and Insects are divergent branches from a common 

 stock. 



FIG. 148. A millipede. 



FIG. 149. A centipede. 



Centipedes and millipedes are characteristically terrestrial. 

 Most are very shy animals, lurking in dark places and 

 avoiding the light, but it is interesting to note that at 

 least two myriopods Geophilus submarines and Linotccnia 

 maritima, occur on British coasts. 



