//. TYPES IN DETAIL IVITH THEIR SUBORDINATE GROUPS. 27 



opening at the base of the legs. 

 Respiration is by tufts of tracheal 

 tubes proceeding from irregularly 

 distributed spiracles. There is 

 but one important genus, Peri- 

 patus. 



Sub-class II. UTSIAFODA Generalized Tracheata, with the 



somites and appendages very sim- 

 ilar to one another; i.e., with little 

 regional differentiation. There is 

 a distinct head, bearing antennae, 

 mandibles, and two pairs of max- 

 illae. 



Order i. Chilopoda Depressed in form; a single pair 



of legs to each somite; mandibles 

 well developed, fitted for predace- 

 ous life; first pair of legs trans- 

 formed into a pair of biting jaws 

 furnished with poison glands. ^. 

 X Lithobius, Scolopendra. 



Order 2 . Diplopoda Usually cylindrical in form, with a 



tendency to coil up when attacked ; 

 the primary somites coalesce in 

 pairs, thus giving an appearance 

 as though there were a double pair 

 of legs to each of the very numer- 

 ous somites. x lulus. 



Sub-class III. HEXAPODA (IitSECTA) . Body divided into three distinct 



regions or somite - complexes : 

 head, thorax, and abdomen; the 

 head bears four pairs of appendages: 

 antennae, mandibles, and two pairs 

 of maxillse; a lost pair appears in 

 some embryos between antennas 

 and mandibles; the thorax bears 

 three pairs of legs and usually two 

 pairs of integumental folds used 



