BUSYCON. 133 



2. Find the slit-like opening that leads from the kidney to 

 the mantle cavity. It is at a point between the two portions of 

 the kidney and is easily found from the mantle chamber. A 

 small opening leads into the pericardium, but it is hard to find 

 it in dissections. 



Digestive System. 1. Remove part of the integument at the 

 base of the proboscis and find the muscles that retract it. How 

 many are there and how are they attached ? Do you understand 

 how the proboscis is extended? 



2. With a pair of scissors open the extended proboscis along 

 the ventral line, pin it open, and notice that the exposed muscu- 

 lar mass, the buccal mass, is attached to the wall of the proboscis 

 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. 



(b) 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 



