THE ARACHNIDS AND THE MYRIAPODS 117 



which secrete a viscous fluid that hardens into silk on 

 exposure to the air. Two trachece (Fig. 58, 8), which give off 

 branches to different parts of the abdomen, open just in front 

 of the spinnerets. 



Many spiders build circular 

 webs of silk, in which they cap- 

 ture insects to suck their blood. 

 A common species of garden 

 spider (Argi'ope ripa'ria) is shown 

 in Fig. 59. The spider first spins 

 a line across the space where the 

 web is to be, and then attaches 

 near its center other threads, 

 which it carries to different points, 

 making the radiating foundation- 

 lines of the web. These lines are 

 all dry and inelastic. Concentric 

 spiral lines of an adhesive nature 

 are then added, the hind legs 

 being used to place the threads, 

 and an oval cover of silk is spun 

 in the center, beneath which, or FlG 5g External Anatomy of th 



' f* "I ~1 1 1 P j 1 "Til 



Spider (Epeira vulgaris). 

 larged. (After Emerton) 



ie 



En- 



in a folded leaf at the side, the 

 spider lurks in watch for its prey. 

 A zigzag band of white silk cross- 

 ing the center is usually added 

 to strengthen the web. When 

 an insect is captured the spider 

 rushes out, and if there is any 

 danger of the escape of the prey, it is deftly wound with 

 more silk till its struggles have ceased. If it proves to be a 

 wasp or other dangerous capture, or if it is too big to be 

 safely managed, it is often assisted to escape by cutting the 

 web, which is then repaired for another victim. 



1, cephalothorax; 2, abdomen; 3, 

 fourth leg; 4, mandible; 5, palpus; 



6, opening to breathing-organ ; 



7, openings to reproductive 

 organs; 8, trachea;; 9, spinnerets 

 (3 pairs) ; 10, anus 



