324 MANUAL OF ZOOLOGY. 



are distinguished by the fact that the abdomen in all is dis- 

 tinctly 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 sepa- 

 rated by the nature of the respiratory organs, the latter breath- 

 ing by tracheae, and not by pulmonary sacs. 



family i. Scorpwnidce. 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. 162, 167). This 



Fig. 167. Scorpion (reduced). 



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 abdo- 

 men is composed of twelve somites, not counting the telson, of 

 which the last five constitute a true "tail" or "post-abdo- 

 men ; " but there is no evident line of demarcation between 

 this region and the cephalothorax. The second segment of 

 the abdomen carries below two curious comb-like organs, of 

 uncertain use, but probably connected with reproduction. The 

 thoracic segments carry four pairs of ambulatory feet. There 

 are six, eight, ten, or twelve simple eyes carried on the top of 

 the head. The maxillary palpi are greatly developed, and 

 constitute strong nipping-claws, or "chelae" (figs. 162, 167). 

 The mandibles (antennae) also form claws, or " chelicerae." 

 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. 162, 3). 



The Scorpions are mostly inhabitants of warm regions, and 

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



