PHYLUM ARTHROPOD A 



373 



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

 not eat solid food. 



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

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



'19 1 



8 10 12 ^^^ss^^s^S^ 



18 



FIG. 314. Diagram of a spider, Epeira diademala, showing the arrange- 

 ment of the internal organs. /, 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 of stomach; Q, cerebral ganglion 

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

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

 form silk glands; 75, tubuliform silk glands; 16, ampulliform silk gland; 

 17, dendriform silk glands; 18, spinnerets; IQ, 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 , * ** 



Spinnerets (Fig. 313; Fig. 314, I#), used 



for spinning threads. The anus (Fig. 

 314, 6) lies posterior to the spinnerets. 



and pencil consisting of 



Hermann.) 



