MACROBDELLA 117 



Preserved specimens if very hard should be placed in 

 water some time before dissection. Cut through the body 

 wall along the mid-dorsal line, being careful not to cut under- 

 lying organs. Lift up the flap of integument and cut the 

 connective tissue loose so it may be turned and pinned back 

 under water. Work forward and backward from the middle 

 of the back. 



1. The digestive tract consists of a buccal pouch, pharynx, 

 stomach, and intestine. 



2. The pharynx is thick walled, elongated, and bound to 

 the body wall by radiating muscle fibers. What is their func- 

 tion? The pharynx is muscular and is provided with bands 

 of longitudinal and with circular muscles. What function is 

 performed by these fibers? 



3. The stomach joins the pharynx, is large, and has di- 

 verticula that nearly fills the body cavity. It occupies a 

 considerable portion of the length of the body. How many 

 pouches has it? Do the pouches bear any relation to the 

 somites? The posterior end of the stomach narrows and pro- 

 jects into the intestine. 



4. The intestine is enlarged a little at its anterior end and 

 tapers posteriorly to a slight dilatation, sometimes called the 

 colon. From this a short rectum runs to the anus. 



Make a sketch of the digestive tract. 



5. Open the digestive tract, wash it out, and examine with 

 a lens. Especially study the pharynx and see how the suck- 

 ing action is produced, and how the blood is forced into the 

 stomach. The cavity of the mouth will be studied later. 



Cut the digestive tract at the rectum and at about the 

 middle of the pharynx and carefully dissect it loose. 



Beneath it notice: 



1. The nerve cord. Do the ganglia have any relation to 

 somites? Find the lateral nerves leaving them. Trace the 

 connectives between them. This will receive more attention 

 later. 



