110 ANNELIDA 



Place a preserved specimen in a dish with a little water. 



1. Note the difference in shape of the two ends of the 

 body. The mouth is at the anterior end, below the protrud- 

 ing lobe of the prostomium. The anus is a vertical slit at 

 the end of the last somite. 



2. How do the ventral and dorsal sides differ? 



3. The right and left sides are symmetrical. Count the 

 somites of the body, compare with others, and record the re- 

 sult. 



4. On the anterior third of the body certain somites are 

 swollen and form the clitellum. What somites are swollen? 

 The clitellum is not present in young individuals. It is used 

 in making egg cases and providing food for developing em- 

 bryos. Understand how this is accomplished. 



5. On the ventral side of the fifteenth somite are small 

 swollen areas where the vasa deferentia open. 



6. Setae project slightly from the surface of each somite. 

 These light colored spines are easily felt with the fingers. 

 See if you can determine the number and position of the rows 

 by stroking gently. How are they used? 



Draw a ventral view of the anterior end, including the 

 clitellum, and another view of the posterior end. 



Taking care not to cut deep, with fine scissors cut through 

 the dorsal wall of the body of a preserved specimen, and ex- 

 tend the cut the whole length of the body. Carefully spread 

 and pin the animal open. In doing this you must tear or cut 

 the septa, but be careful not to tear or break the organs that 

 perforate them. 



Alimentary Canal. — This consists of a straight tube that 

 runs the length of the body. 



1. Immediately behind the mouth is a muscular, white 

 organ, the pharynx. Through how many somites does this 

 extend? It is connected with the body wall by numerous, 

 radiating muscle fibers. What function do these fibers per- 

 form? 



2. Behind the pharynx is the narrow and long esophagus. 

 This runs posteriorly between lobed, light colored organs, the 



