ARTICULATA. 225 



the Cheese -mite, the Itch -insect, and many similar 

 forms. The Ticks (Ixodes) have a piercing beak and a 

 leathery skin. 



2.) Pedipalpi, or Scorpions, have maxillary palpi ending 

 in forceps, and a prolonged jointed abdomen. (Fig. 127.) 

 Breathing takes 

 place by pulmo- 

 nary sacs, similar 

 to spiders. The 

 nervous and cir- 

 culatory systems 

 are highly organ- 



, rr , , FIG. 127. Scorpion. 



ized. The last 



joint of the abdomen bears in scorpions a sharp spine at 

 its end, perforated by the duct of a poison-gland, 

 whereby it inflicts painful wounds. The Chelifer, or 

 Book-scorpion, sometimes found in old books, has no 

 sting. The Phalangers, or Harvest-spiders, with long 

 hooked palpi and long ungainly legs, belong to this 

 order. 



3.) Araneida, or Spiders, have the cephalo-thorax 

 joined to the sac-like abdomen by a narrow constriction, 

 and are provided at the posterior end with two or three 

 pairs of appendages called "spinnerets." The use of the 

 spinnerets is to reel out the silk for their web from the 

 silk-glands. The tip of each is perforated by many pores, 

 through which the silk escapes, so that each thread of 

 the web may consist of several hundred strands. The 

 silk is fluid at first, but rapidly hardens. The hind feet 

 have comb-like claws for pressing the silk together. 

 Sometimes one pair of the hinder appendages consists 



