43 



THE ODONTOPHOBE. 



The complex odontophore of the whelk was examined 

 by Geddes in 1878. He does not describe the structures 

 in detail, but gives figures of some dissections. 



In order to expose this organ, the proboscis should 

 be removed and pinned down with the dorsal surface 

 uppermost. If a cut is made down the middle line and 

 the flaps folded back, the whole apparatus lies somewhat 

 as figured in PL III, fig. 19, the^oesophagus resting on 

 the odontophore. 



Now the odontophore consists essentially of a band 

 (the radula), to which are attached a large number of 

 muscles. This band is fixed, pulley-like, on a grooved 

 support, which we shall call the odontophoral cartilage. 

 The whole structure is bound together by two delicate 

 sheets of transverse muscle fibres. One of these will be 

 seen immediately the oesophagus is removed, and lies 

 dorsally, forming a roof over the radula and cartilage 

 (fig. 19, d.m.s.). Two dorsal protractor muscles (fig. 19, 

 d. pr. m.) run from the anterior end of the proboscis 

 walls to the odontophore. In addition to these, the walls 

 of the buccal cavity are muscular, and there are two 

 delicate ventral protractor muscles (fig. 18, v. pr. m.). 

 It seems probable that protrusion of the odontophore (it 

 can be brought up to the mouth opening), is aided by 

 blood pressure, in addition to muscle action. 



A conspicuous central dorsal muscle (figs. 19 and 16, 

 C.d.m.), which is attached to the extremity of the radula 

 (dorsally), extends back over a large number of other 

 muscles, all of a faint red tint, to become attached to 

 the floor of the proboscis. At the sides of these muscles 

 are two peculiar straps, consisting of a connective tissue 

 matrix with numerous muscle fibres (figs. 16, 18, 19, 20, 



D 



