MYRIAPODS. 



127 



SUB-CLASS III. MYRIAPODA. 



The group of centipedes, niillipetls, and thousand-legged worms, receives both its 

 scientific and popular names from the large number of locomotive organs possessed by 

 the various individuals. In scientific terms myriapods may 

 be defined as terrestrial arthropods, with distinct head and 

 numerous similar post-cephalic segments; there is a single 

 pair of antennas, and two pairs of jaws ; the legs are num- 

 erous, and the respiration is by trachea. 



In external form, as well as internal structure, the myria- 

 pods present many similarities to the larva? of the hexapods. 

 The nervous system is composed of a long series of similar 

 ganglia, one to each segment. The digestive canal, with rare 

 exceptions, pursues a straight course through the body. The 

 long heart extends through all the body segments and forces 

 the blood forward. In some forms the mouth-parts are adapted 

 for sucking. Ocelli are visually present. The young hatch 



J J FIG. 185. Young myriapod 



from the egg with a varying number of appendages, many (Stnmgyiosoma), just 



having but three pairs, thus showing a marked resemblance 



to the larvae of many of the hexapods. Three well-marked groups are found. 



ORDER L CHILOGNATHA OR DIPLOPODA. 



These are the millipeds proper. The body is round or flattened, the feet are 

 inserted close together, and all the segments behind the third bear two pairs of limbs. 

 They frequent dark places, and feed largely on decaying vegetation. Many have the 

 power of curling themselves in a spiral when disturbed. 



The POLYZONID.E have a very small head; the mouth-parts are united so as to 

 form a sucking tube, and the eyes are few or wanting. The IULID^S have a large head, 

 free mouth-parts, and a cylindrical body. The various species of lulus are known as 

 galley worms, and are not uncommon in decaying timber and similar locations. When 

 disturbed they coil themselves into a spiral like a watch-spring, and also emit a strong 

 odor. This is produced by glands inside the body Avhich open on the sides of the seg- 

 ments, the small openings superficially resembling spiracles. The odor is evidently a 



provision for defence. In 1. canadensis, a 

 chestnut-colored species with a black dorsal 

 band, these openings are ringed with black, 

 thus making them more prominent. The 

 LYSIOPETALID^E are closely related to the 

 luHdaB. They have numerous ocelli, except 

 in the blind forms, and seven-jointed an- 

 tennae, and the body is constricted behind the head. The forms are mostly small. 

 We figure Scoterpes copei, a blind form found in Mammoth Cave. 



The POLYDESMID^; have the sides of the segments expanded in broad plates, and 

 the segments themselves are comparatively few. The POLYXEOSTID^; embraces forms 



