ANNULOSA : ARACHNIDA. 203 



from the abdomen. The mandibles in Galeodes, which is the 

 type of the group, are chelate, but the maxillary palpi consti- 

 tute long feet. 



DIVISION B. PULMOXABIA. Respiration by pulmonary sacs 

 alone, or by pulmonary sacs conjoined with trachece. Eyes six 

 or more in number. Abdomen usually distinct from the ceplia- 

 lothorax. 



This division comprises the higher Arachnida, such as the 

 Scorpions, and the majority of what are commonly known as 

 Spiders ; the former constituting the order of the Pedipalpi, 

 the latter that of the Araneida or Dimerosomata. 



ORDER I. PEDIPALPI. In this order are the true Scorpions, 

 together with certain other animals which are in some respects 

 intermediate between the Scorpions and the true Spiders. The 

 members of this order are distinguished by the fact that 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 1. 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 (fig. 57, 2). 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 is no evident line of de- 

 marcation between this region and the cephalothorax. The 

 thoracic segments carry four pairs of ambulatory feet. The 

 maxillary palpi are greatly developed, and constitute strong 

 nipping claws, or 'chelae' (fig. 57, 1). The mandibles (an- 

 tennae) 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. 57, 3). 



The Scorpions are mostly inhabitants of warm regions, and 

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

 nature. 



Family 2. Thelyphonidce. The members of this family in 

 external appearance closely resemble the true Spiders, from 

 which they are separated by the possession of a segmented 

 abdomen and long, spinose palpi, and by the absence of spin- 

 nerets. They are distinguished from the Scorpionidce, by the 



