ARTHEOPODA. 



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long, tail-like abdomen and the abnorrtial jaws place them 

 in a lower rank. The abdomen consists of twelve seg- 

 ments : the anterior half is as large as the thorax, with no 

 ■well-marked division between ; the other part is compara- 

 tively slender, and ends in a hooked sting, which is perfo- 

 rated by a tube leading to a poison-sac. The mandibles 

 are transformed into small, nipping claws, and the eyes 

 generally number six. Kespiratjon is carried on by four 

 pairs of pulmonary sacs which open on the under surface 



Pio. 259 Scorpion (nndei surface) and Centipede. 



of the abdomen. The heart is a strong artery, extending 

 along the middle of the back, and divided into eight separate 

 chambers. Scorpions are confined to the warm-temperate 

 and tropical regions, usually lurking in dark, damp places. 



The Harvest-men {Phalangium), frequently seen about 

 our houses, belong to this order. They have a short, thick 

 body and extremely long legs, and breathe by tracheae. 



3. Araneina, or Spiders. They are distinguished by 



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