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. Pedijpaljpi , 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 
