PHYLUM ARTHROPODA 



373 



illae) ; it serves for the ingestion of juices only, since spiders do 

 not eat solid fo6d. 



The abdomen is connected by a slender waist with the cephalo- 

 thorax. Near the anterior end of the abdomen on the ventral 



22 



Fig. 314. — Diagram of a spider, Epeira diademata, showing the arrange- 

 ment of the internal organs. 1, mouth; 2, sucking stomach; 3, ducts of liver; 

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

 of sucking stomach; 8, caecal prolongation ot stomach; q, cerebral ganglion 

 giving off nerves to eyes; 10, subcesophageal ganglionic mass; //, heart with 

 three lateral openings or ostia; 12, lung sac; 13, ovary; 14, acinate and pyri- 

 form silk glands; 15, tubuliform silk glands; 16, ampulliform silk gland; 

 17, dendriform 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 the Cambridge Natural History.) 



surface is the genital opening, protected by a pair of appendages 

 which have fused together to form a plate called the epigynum 

 (Fig. 313). On either side of the epigy- 

 num is the slit-like opening of the respir- 

 atory organs or lung books (Fig. 313; 

 Fig. 314, 12). Some spiders also possess 

 trachea which open to the outside near 

 the posterior end on the ventral surface 

 (Fig. 313). Just back of the tracheal Fig. 315. — End of foot 

 opening are three pairs of tubercles or °* p * ^wing^ *™ daws 



Spinnerets (Fig. 313; Fig. 314, 18), used and pencil consisting of 

 r„ •__• 4.1. j rpu /"!?• spatulate hairs (5). (From 



for spinning threads. The anus (Fig. s P edgwick , s Zoo \ ; gy ; after 

 314, 6) lies posterior to the spinnerets. Hermann.) 



