SYCOTYPUS. 113 



(c) 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. 



(d) 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. 



(e) 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 

 cartilage so the teeth are turned in. What reason is there for 

 folding the radula in this manner? 



(/) Cut the cartilage protractors and reflect the buccal mass. 

 It is attached to the wall of the proboscis at its posterior end by 

 strong muscles, the radula retractors. These may be studied 

 after cutting the sheath of cross-fibers that hold the mass together. 

 Determine how they are attached to the sides of the radula. 

 Why do they need to be so powerful ? 



(g) The retractors of the cartilage are attached to the ends 

 of the horns and extend posteriorly to the walls of the proboscis. 



Make a drawing of the buccal mass as seen from the dorsal side. 



(fi) Pull away the muscles and examine the shape of the 

 odontophoral cartilage and its relation to the radula. 



(i) Remove the radula, unfold it, and examine it microscop- 

 ically. Do the teeth differ in any way at the two ends? Why 

 is the radula so long? 



Draw a portion. 



The radula is the organ upon which most gastropods depend 

 for getting food. You should understand how: 



1. The proboscis is protruded and retracted. 



2. The odontophoral cartilage is protruded and retracted. 



3. The radula is protracted and retracted. 



4. The radula is folded by the cartilage and spread for action. 



5. The food is torn off and taken into the mouth. 



Near the base of the proboscis is a pair of large, 3^ellow 

 8 



