288 



COMPARATIVE ZOOLOGY. 



ticulates. The body is soft and minute. The Ticks 

 {Ixodes) have a leathery skin, and are sometimes half an 

 inch long. The mouth is furnished with a beak for pierc- 

 ing the animal it infests. 



2. Pedipalpi, or Scorpions, characterized by very large 

 maxillary palpi ending in forceps, and a prolonged, joint- 

 ed abdomen. The nervous and circulatory systems are 

 more highly organized than those of Spiders; but the 

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



Fig. 259 Scorpion (under surface) and Centipede. 



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. Respiration is carried on by four 

 pairs of pulmonary sacs which open on the under surface 



