164 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



(iii.) The posterior end of the " stomach " forms a small 

 papilla which projects into the " intestine." 



4. The "intestine" enlarges a little, near its anterior 

 end, and then tapers gradually to the anus. 



5. Make a sketch of the digestive tract, showing these 

 points. 



b. Cut through the middle of the dorsal wall of the 

 digestive tract, with a pair of scissors, in order to expose 

 the interior. Wash out, with a stream of water, any food 

 which may remain in the stomach ; and, examining the 

 various regions with a lens, notice : 



1. The pharynx. Its walls are very thick and mus- 

 cular, and are joined to the integument by radiating mus- 

 cles, which, by distending its cavity, produce a sucking 

 action. 



2. The cavity is largest in the middle, and opens into 

 the stomach through a small round aperture surrounded by 

 muscles. 



3. Six or eight large longitudinal bundles of muscles 

 give to the inner wall of the pharynx a plicated appear- 

 ance. By the action of these muscles the blood which has 

 been sucked into the pharynx by the contraction of the 

 radiating muscles, is driven backward into the sacculi of 

 the stomach. 



4. Each sacculus is divided, on each side the middle line, 

 into an anterior and a posterior chamber. The posterior 

 chamber is the larger, and is prolonged downwards and 

 backwards. 



5. The posterior chambers of the last or eleventh saccu- 

 lus are much larger than the others, and run backwards to 

 form two large horn-like diverticula, which reach nearly 

 to the posterior end of the body. 



6. Between the anterior ends of these diverticula the 



