XIV. SCORPIONS, SPIDERS, AND TICKS 



Arthropoda {corUinued) 



Class. — Arachnida (arachne, spider) 



Although these animals are closely related to the crus- 

 taceans, they differ from the latter, in not having their 

 bodies inclosed by a calcareous crust. They differ also in 

 living, with few exceptions, on land. The more familiar 

 examples of this class are the spiders, present everywhere, 



the ticks, on cattle 



and dogs, and the 

 mites on fowls and 

 plants. 



Scorpions. — Al- 

 though these ani- 

 mals are thought to 

 be very venomous, 

 it is difficult to find 

 an authentic case of 

 deatli by a scor- 

 pion's sting. The 

 larger species in the 

 tropics, liowever, cause soilous wounds. The liody of the 

 scorpion is divided into two distinct regions, the cephalo- 

 thorax and the abdomen. The abdomen consists of an 

 enlarge<l poi'tion, next to the thorax, called tlu^ jircnlidnmcn, 

 and a long, slender taildike portion, the poslahdomcn (Fig. 

 82). The scorpion has two pairs of jaws and to one pair 



144 



Fig. 82, 



' Scorjji 



