66 Invertebrate Zoology. 



Draw. 



The odontophoral or radular protractors are muscle 

 fibres which extend from the lower side of the muscular 

 mass to the inner surface of the integument, near the free end 

 of the proboscis. The radular retractors are a series of 

 fibres extending dorsally from the proximal end of the 

 cylinder to the inner surface of the integument, near the 

 base of the proboscis. 



Having opened the oesophagus, free it from the underlying 

 muscular mass, and note the transverse fibres of a thin 

 muscle sheet that rested below the middle third of the 

 oesophagus and gives attachment to the radular protractors 

 along its lateral edge. Observe that the radula extends 

 under the muscle from near the base of the proboscis to its 

 free end, and that the obliquely disposed radular retractors 

 also extend under the muscle sheet. 



Carefully slit open the muscle sheet and note the place of 

 insertion of the radular retractors along the sides of the 

 radula. 



The lower surface of the radula rests upon a pair of 

 elongated odontophoral cartilages, the retractor muscles 

 of which extend proximally and below the radular retractors 

 to a tendinous ring, which also gives attachment to the white 

 fibres of the retractors of the proboscis. On the ventral 

 side of the muscular mass the ventral retractor of the radula 

 will be noted. It is a small muscle, lying between the 

 odontophoral cartilages, and by its contraction the dorsal 

 surface of the radula is brought down over the pulley-like 

 ends of the odontophoral cartilages. 



Make a drawing that will illustrate the structure of the 

 radular apparatus. 



The oesophagus passes between the mass of white re- 



