214 



FUNCTIONS AND POSITION OF RADULA 



tion of the jaw, it comes within the province of the radiila, the 

 front part of which perhaps co-operates to a certain extent with 



Fig. 110. — Jaws o^ Sepia: A, in siiu, 

 witliin the buccal mass, several of 

 the arms having been cut ' away ; 

 B, removed from the mouth and 

 slightly enlarged. 



Fic. 111. — Patella vulgata L., show- 

 ing the normal position of the 

 radula, which is doubled back in 

 a bow ; the shell has been re- 

 moved, and the whole visceral 

 mass is turned forward, exposing 

 the dorsal surface of the muscular 

 foot : gr, longitudinal groove on 

 this surface ; i, i, intestine ; /, 

 liver ; m, m, mantle edge ; imi, 

 muscles (cut through) fastening the 

 visceral mass to the upper sides of 

 the foot ; 0!', ovary ; r, radula; u.f, 

 \\\)-p&v or dorsal surface of the foot. 



the jaw in performing the Ijiting process. The fnnction of the 



where the radula is almost filmy in its transparency, like those of Actacon and the 

 small Scalar in. 



"When once the radula is laid out, the mounting is commonly easy. Canada 

 balsam makes it too transparent. Fluids may be used, and are almost necessary for 

 thick radulae like those of large Chitons ; but the best general medium is glycerine 

 jelly. It runs under the cover glass by capillary attraction, and may be boiled 

 (though only for a moment) to get rid of air bubbles. It should then be left im- 

 finished for several week.s. If cracks appear, the reason is either that the jelly is a 

 bad sample, or that it has been boiled too long, or (commonly) that the object is too 

 thick ; and there is not often any difficulty in remounting. I have no serious com- 

 plaint of want of permanence against the medium, if I may speak from a pretty 

 wide experience during the last twenty years." 



