CLASSIFICATION 



Arachnida. Terrestrial. Usually two regions, cephalo- 

 thorax and abdomen; though various Acarina have but one 

 and Solpugida have all three head, thorax and abdomen. 

 Cephalothorax unsegmented, bearing two pairs of oral append- 



FIG. 3. 



FIG. 4. 



Peripatus capensis. Natural size. After MOSELEY. 



ages and four pairs of legs. Abdomen segmented or not, 

 limbless. Respiration tracheal, by means of book-leaf tra- 

 ' cheae, tubular tracheae, or both ; stigmata almost always abdom- 

 inal, at most four pairs. Heart abdominal in position. 

 Example, Buthus (Fig. 2). 



Malacopoda.-- Terrestrial. 

 Vermiform (worm-like), unseg- 

 mented externally. One pair of 

 antennae, a pair of jaws and a 

 pair of oral slime papillae. Legs 

 numerous, paired, imperfectly 

 segmented. Respiration by means 

 of tubular tracheae, the stigmata 

 of which are scattered over the 

 surface of the body. Numerous 

 nephridia (excretory) are pres- 

 ent and these are arranged seg- 

 mentally in pairs. Two separate 

 longitudinal nerve cords, con- 

 nected by transverse commissures. Integument delicate. A 

 single genus, Peripatus (Fig. 3), comprising many species. 



Diplopoda. Terrestrial. Two regions, head and body. 

 Body usually cylindrical, with numerous segments, most of 

 which are double and bear two pairs of short limbs, which are 

 inserted near the median ventral line. Eyes simple, antennae 



A diplopod, Spirobolus marginatus. 

 Natural size. 



