x PHYLUM ARTHROPODA 253 



acter than that of the Insecta. The heart is in the form 

 of a long tube consisting of as many chambers as there are 

 segments in the body. The breathing organs are air-tubes 

 or tracheae resembling those of Insects. 



5. THE ARACHNIDA 



The class Arachnida, comprising the Scorpions and 

 Spiders, the Mites and Ticks, the King-Crabs, and a number 

 of other families, is a much less homogeneous group than the 

 Insecta, resembling the Crustacea in the variety which it 

 presents in the arrangement of the segments and their 

 appendages. In most members of the class, however, there 

 is an anterior region of the body the cephalothorax repre- 

 senting both head and thorax, and a posterior part or 

 abdomen, which is typically composed of a number of 

 distinct segments; in some cases the cephalothorax and 

 abdomen are united. 



Scorpions are inhabitants of warm countries the largest 

 kinds being found in tropical Africa and America. They 

 are nocturnal animals, remaining in holes and crevices 

 during the day, and issuing forth at night to hunt for their 

 prey, which consists of Spiders and Insects. These they 

 seize with the pincer-claws and sting to death with the 

 caudal spine, afterwards sucking their juices. 



There are a number of different species of Scorpions, 

 divided into several genera, which differ from one "another 

 in comparatively unimportant points, so that the following 

 general description will apply almost equally well to any of 

 them. 



A Scorpion (Fig. 140) has a long narrow body, in super- 

 ficial appearance not unlike that of a Crayfish. There is a 



