242 MANUAL OF ZOOLOGY. 



the abdomen in all is distinctly segmented, but is not separated 

 from the cephalothorax by a well-marked constriction. They 

 agree in this character with the Adelarthrosomata ; hence the 

 two are sometimes united into a single order (Arthrogastra), 

 but they are separated by the nature of the respiratory organs, 

 the latter breathing by tracheae, and not by pulmonary sacs. 



Family i. Scorpionidce. — The Scorpions are amongst the best 

 known of the Arachnida, as well as being amongst the largest. 

 They are distinguished by their long, distinctly segmented ab- 

 domen, terminating in a hooked claw (figs. 77, 79). This claw, 

 which is really a modified "telson," is the chief offensive weapon 

 of the Scorpion, and is perforated at its point by the duct of a 

 poison-gland which is situated at its base. The abdomen is 

 composed of twelve somites, but there isi no evident line of de- 

 marcation between this region and the cephalothorax. The 

 thoracic segments carry four pairs of ambulatory feet. There 

 are six, eight, or twelve simple eyes. The maxillary palpi are 



Fig. 79. — Scorpion (reduced). 



greatly developed, and constitute strong nipping - claws, or 

 "chete" (figs. 77, 79). The mandibles (antennae) also form 

 claws, or " cheUcerae." The respiratory organs are in the 

 form of pulmonary sacs, four on each side, opening upon the 

 under surface of the abdomen by as many stigmata, each of 

 which is surrounded by a raised margin, or "peritrema" (fig. 



77, 3)- . 



The Scorpions are mostly inhabitants of warm regiqps, and 

 their sting, though much exaggerated, is of a very severe 

 nature. They live under stones or in dark crevices, and run 

 swiftly, carrying the tail curved over the back. They feed on 

 Insects, which they hold in the chelate palpi and sting to 

 death. 



Family 2. TTielyphonida. — The members of this family in 



