CHAPTER XII 



ARACHNIDA {CONTIXUED) EMBOLOBKANCHIATA SCOEPIONIDEA 



PEDIPALPI 



SUB-CLASS II.— EMBOLOBEANCHIATA.i 



Order I. Scorpionidea. 



Segmented Arachnids with chelate chelicerae and pedipalpi. 

 The abdomen, which is broadly attached to the cephalothorax or 

 prosoma, is divided into two regions, a six-jointed mesosoma atid a 

 six-jointed tail-like metasoma, ending in a poison-sting. There 

 are four pairs of lung-books, and the second mesosomatic segment 

 bears a pair of comh-like organs, the pectines. 



The Scorpions include the largest tracheate Arachnid forms, 

 and show in some respects a high grade of organisation. It is 

 impossible, however, to arrange the Arachnida satisfactorily in an 

 ascending series, for certain primitive characteristics are often 

 most marked in those Orders which on other grounds would seem 

 entitled to rank at the head of the group. Such a primitive 

 characteristic is the very complete segmentation exhibited by the 

 Scorpions. They are nocturnal animals of rapacious habit. In 

 size they range from scarcely more than half an inch to eight 

 inches in length. In the northern hemisphere they are not 

 found above the fortieth parallel of latitude in the Old "World, 

 though in the New World they extend as high as the forty-fifth. 

 A corresponding southward limit would practically include 

 all the land in the southern hemisphere, and here the Order is 

 universally represented except in New Zealand, South Patagonia, 

 and the Antarctic islands. 



■i Cf. p. 258. 

 297 



