612 ZOOLOGY SECT. 



pair of legs terminate in a many-jointed flagellum. The organs 

 of respiration are two pairs of book-lungs on the second and third 

 segments of the abdomen. 



This order includes the Scorpion-spiders (Fig. 503). 



ORDER 4. SOLPUGIDA, 



Arachnida with three regions head, thorax (of three segments), 

 and abdomen (of ten segments). The chelicerae are chelate ; the 

 pedipalpi elongated and leg-like. The organs of respiration are 

 tracheae. 



This order includes Gfaleodes (Fig. 504). 



ORDER 5. PHALANGIDA. 



Arachnida with an unsegmented cephalothorax, and an abdomen 

 of six segments. The chelicerae are chelate, the pedipalpi leg-like. 

 The organs of respiration are tracheae. No spinning glands are 

 developed. 



This order includes the Harvest-men. 



ORDER 6. ARANEIDA. 



Arachnida in which the body is composed of an undivided 

 cephalothorax and an unsegmented abdomen, which is usually soft 

 and rounded, and attached to the cephalothorax by a narrow neck. 

 The chelicerae are sub-chelate, with poison glands ; the pedipalpi 

 simple. The organs of respiration are book-lungs alone, or book- 

 lungs combined with tracheae. 



This order comprises all the true Spiders (Fig. 505). 



ORDER 7. ACARIDA. 



Arachnida in which the body exhibits no division into regions. 

 The mouth-parts are adapted either for biting or piercing and 

 sucking. The organs of respiration, when present, are in the 

 form of tracheae. 



This order includes the Mites and Ticks (Figs. 508 and 509). 



ORDER 8. XIPHOSURA. 



Arachnida in which the body consists of a cephalothorax, 

 covered over by a broad carapace, and an abdomen of seven 

 firmly united segments, with a long narrow tail-piece or telson. 

 The cephalothorax bears a pair of short chelate appendages 

 and five pairs of legs. The abdomen bears in front a pair of 

 united plate-like appendages, forming the operculum, followed 

 by five pairs of flat appendages overlapped by the operculum. 

 The organs of respiration are lamelliform gills attached to the 

 abdominal appendages. 



This order includes the King-crabs (Limulus) (Fig. 510). 



