PHYLUM ARTHROPODA 377 



secreted by a number of abdominal silk glands (Fig. 314, 14-17], 

 passes to the outside and hardens in the air, forming a thread. 

 These threads are used to build nests, form cocoons, spin webs, 

 and for many other purposes. An orb web, such as is shown in 

 Figure 3 16, is spun in the following manner. A thread is stretched 

 across the space selected for the web; then from a point on this 

 thread other threads are drawn out and attached in radiating 

 lines. These threads all become dry and smooth. On this 

 foundation a spiral is spun of sticky thread. The spider stands 

 in the center of the web or retires to a nest at one side and waits 

 for an insect to become entangled in the sticky thread; it then 

 rushes out and spins threads about its prey until all struggles 

 cease. 



Many spiders do not spin webs, but wander about capturing 

 insects, or lie in wait for them in some place of concealment. In 

 this group belong the crab-spiders (THOMISID^E, Fig. 317, A), 

 jumping- spiders (AxxiD^;, Fig. 317, B), ground-spiders (DRAS- 

 SID^E), and running spiders (LYCOSID.E, Fig. 317, C). The cob- 

 web spiders spin various kinds of nets for capturing insects. The 

 tube-weavers (AGELENID,E) build platforms on the grass and 

 hide in a tube at one side; the line weavers (LINYPHIAD^E) spin 

 flat webs with irregular meshes; the round-web spiders (EPEIRI- 

 build webs like that shown in Figure 316; and theTHERi- 

 (Fig. 317, D) build irregular webs in corners and on plants. 



b. Other Arachnida 



Order 2. Scorpionidea. -- SCORPIONS. - -The scorpions are 

 rapacious arachnids measuring from half an inch to eight inches 

 in length. They live in tropical and subtropical regions, hiding 

 in crevices or in pits in the sand during the daytime, but running 

 about actively at night. They capture insects and spiders with 

 their pedipalpi (Fig. 318), tear them apart with their chelicerae, 

 and devour the pieces. Larger animals are paralyzed by the 

 sting on the end of the tail. This sting does not serve as a weapon 

 of defense unless the scorpion is hard pressed; and is not used, as 



