CHAPTER XIII 



THE SUBPHYLUM MYRIAPODA 



Land-living tracheate arthropods, usually elongated, with numerous 

 leg-bearing segments; a distinct head with a single pair of antennae, 

 a palpless mandible and at least one pair of maxillae ; tracheal system 

 with segmentally repeated stigmata, tracheae usually anastomosing; 

 eyes, if present, clumps of ocelli; mid gut without special digestive 

 glands, end gut with Malpighian tubules ; young hatching at a stage 

 resembling the adult but possessing fewer than the adult complement 

 of segments. 



It has long been recognized that the group Myriapoda as defined 

 above contains two chief divisions which are here treated as classes, 

 one of which, the Chilopoda, is more closely related to the Insecta than 

 the other, the Diplopoda. It is, however, convenient to retain the 

 group, though the similarity of the chief members is probably more 

 superficial than natural. 



Classification. Chilopoda (Opisthogoneata), centipedes; Diplo- 

 poda, millipedes (with two smaller classes, the Symphyla and the 

 Pauropoda, these form the Progoneata, all distinguished by having 

 the genital opening near the anterior end of the body). 



Class CHILOPODA 



Carnivorous arthropods with the genital opening situated at the hind 

 end of the body (opisthogoneate) ; body segments all similar (at least 

 in the more primitive members of the division), body usually flattened 

 dorsoventrally ; ocelli present, head bears also antennae and three 

 pairs of jaws (mandibles and two pairs of maxillae); the ist body 

 segment bears a pair of poison claws ; the rest, each a single pair of 

 ambulatory limbs, except the last two, which are legless ; blood system 

 consists of a dorsal heart and a ventral vessel connected by an anterior 

 pair of aortic arches ; tracheae typically branch and anastomose and 

 have a spiral lining ; gonads dorsal to gut. 



The type used for the study of this division is the centipede, 

 Lithobius (Fig. 280), which is found under bark and stones, and is 

 a much more active creature than the millipede, lulus, which is found 

 in the same situation. The chitinous exoskeleton is flexible and is fre- 

 quently moulted. The body is flattened dorsoventrally and the legs in 

 each pair are widely separated. The head consists of six segments all 

 represented by coelomic sacs in the embryo which disappear in the 

 adult, including 3.preoral and (between the antennae and the mandibles) 



