254 MANUAL OF ZOOLOGY sf.ct. 



each specially organised for the part which it has to play in 

 the economy of the community. 



5. THE ARACHNIDA 



The 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, 

 approaching 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 dis- 

 tinct segments ; in some cases 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 under stones or 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 their pincer-claws and sting to death 

 with their 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. 151) has a long narrow body, in super- 

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

 small cephalothoracic shield or carapace, covering over dor- 

 sally a short anterior region or cephalothorax. This is followed 

 by a long posterior region or abdomen, the terminal part 



