PHYLUM ARTHROPOD A 



265 



known from the United States, but there are species in 

 Mexico, South and Central America, and the West Indies, 

 and no fewer than five inhabit the Isthmus of Panama. 



Class Diplopoda 



The millipedes, usually with long cylindrical bodies, Millipedes 

 and most of the segments bearing two pairs of legs. 

 They move slowly, and usually curl up when alarmed. 

 The surface of the body is typically smooth or tubercu- 

 lated, often shiny. A very ancient fossil form (Palcso- 

 campa, from Mazon Creek, Illinois) was profusely 

 hairy, and the curious little Polyxenus, still living in 

 various parts of the world, is hairy. In Mexico and 

 other southern countries very large millipedes, as long 

 as a finger, may be found. The millipedes and centi- 

 pedes have commonly been classed together as a great 

 group Myriapoda (many or myriad legs), but they are 

 really very distinct groups, though agreeing in the single 

 pair of antennae and the numerous segments and legs. 







FIG. 78. Two millipedes. 



tic. 79. Dorsal and ventral views of 

 a common centipede. 



