BUSYCON. 



137 



in the region of the mouth, at its base, and by means of fibers, 

 along its sides. 



3. Push the muscular mass slightly to one side and notice 

 the esophagus, which is closely applied to the dorsal wall of the 

 proboscis. Notice the muscle fibers that extend from it to the 

 proboscis. What is their function? 



4. The odontophoral apparatus consists of a forked cartilage, 

 the odontophoral cartilage, that is surrounded by muscles and 

 cannot be seen until these are removed, a radula which is for 

 most of its length enclosed in a sac, the radular sac, and is ex- 

 posed only in the region of the mouth, and the muscles for mov- 

 ing the cartilage and the radula. 



(a) The strands of muscles that run from its sides forward 

 to be inserted on the walls of the proboscis are attached to the 

 odontophoral cartilage. These are the cartilage protractors. 



(h) Attached to the ends of the two horns of the cartilage 

 and running posteriorly to be attached to the walls of the pro- 

 boscis near its base are the flat cartilage retractors. 



(c) Running lengthwise of the buccal mass, on its ventral 

 side, are three pairs of slender muscles, one pair median and the 

 others covering the horns of the odontophoral cartilage that has 

 just been observed. Find to what the muscles are attached 

 anteriorly and posteriorly. If the animal is fresh, pull on them 

 with the forceps and see what moves. These are the radula 

 protractors. 



(d) Beneath the radula protractors observe the sheet of cross- 

 fibers that bind the horns of the odontophoral cartilage together. 



Make a drawing showing the ventral side of the buccal mass. 



(e) A portion of the radula is visible near the anterior end of 

 the proboscis. Introduce a bristle into the esophagus and deter- 

 mine its relation to the exposed radula. 



(/) Loosen the anterior end of the buccal mass from the wall 

 of the proboscis, turn it back and see how the radula passes 

 around the odontophoral cartilage. With a hand-lens notice 

 the teeth on the open radula, ventral to the cartilage, and see 

 how the radula is folded as it passes over the dorsal side of the 



