202 



ARTHROPODA 



parts. The mandibles or chelae are large and end in a slender, 

 sharp-pointed hollow fang, through which poison flows. The palpi 

 {pedipalpi) are sometimes half as long as the legs. 



The trap door spiders^ Cteniza^ dig tunnels, line them with silk. 



13 ^2 14 18 



Fig. 94. Internal anatomy of a spider. /, mouth; 2, sucking stomach; j, ducts 

 of liver; 4, so-called malpighian tubules; 5, stercoral pocket; 6, anus; 7, dorsal muscle 

 of sucking stomach; <?, caecal prolongation of stomach; g, cerebral ganglion giving off 

 nerves to eyes; 10, suboesophageal ganglionic mass; //, heart with three lateral openings 

 or ostia; 12, lung sac; /J, ovary; 14, 15, 16, 17, silk glands; 18, spinnerets; ig, distal 

 joint of chelicera; 20, poison gland; 21, eye; 22, pericardium; 23, vessel bringing blood 

 from lung sac to pericardium; 24, artery. (From Sedgwick, Textbook oj Zoology. 

 Courtesy of Macmillan and Co., Ltd.) 



and equip them with a 

 hinged lid. The ground 

 spiders., Drassidae, deposit 

 their eggs in silken tubes 

 and do not spin a web. 

 The jimnel web weavers, 

 Agalenidae, weave concave 

 sheets of silk with a funnel 

 on one side, attaching the 

 web to blades of grass by- 

 threads. After a heavy 

 dew, the webs are conspic- 

 uous on the lawn or in the 

 field. The cobweb weavers 

 ( Theridiidae) are small, 

 light-colored forms, hang- 

 ing downward from shape- 



FlG. 



95- 



Epeira, a garden weaver. 

 A. M. Reese.) 



(Photo by 



