PHYLUM ARTHROPODA — CLASS ONYCHOPHORA 



289 



of legs and two pairs of spiracles. The spiracles are closed by a valve 

 and communicate with tracheal pockets and unbranched tracheae. 

 Embryological evidence supports the belief that the abdominal seg- 

 ments have resulted from the fusion of two segments. 



The legs are jointed very much as in the insects. The tarsus con- 

 sists of the three segments. 



The heart is a dorsal structure with side valves and an anterior 

 tube to the head similar to the arrangement in the insects. The di- 

 gestive tract consists of a mouth, esophagus, stomach, and intestines. 

 The excretory wastes of the body are removed by two or four pairs 

 of Malpighian tubules which discharge their excretions into the in- 

 testines. 



th 



Fig. 164. Julus terrestris. A common millepede. Side view of anterior end. 

 a, antenna; ab. abdomen; colj collum (first thoracic segment) ; e, a group of 

 ocelli ; g, gnathochilarium ; go, genital opening ; h, head ; I, labium ; m, mandible ; 

 th, thorax. (After Borradaile and Potts, Invertebrata. Redrawn by Nelson A. 

 Snow.) 



The millepedes feed upon vegetable matter, decaying as well as 

 living plant substance. They are slow-moving, wormlike creatures, 

 living in dark, moist places. When disturbed they usually roll them- 

 selves up into a little coil. The eggs are laid in damp earth, and 

 when the young hatch they are very small, consisting of only a few 

 segments and three pairs of legs. 



The diplopods are found in most parts of the world. In the United 

 States there are six important families and about 120 species. The 

 family Julidae is widely distributed. The species Julus hortensis 

 Wood; J. virgatus; J. hesperus Chamberlin; and Spiroholus margin- 



