442 



MOLLUSCS \ND BRACHIOPODS. 



The radula itself is a band or ribbon of varying length and 

 breadth, formed of chitin, generally almost transparent, some- 

 times beautifully coloured, especially at the front end, with red or 

 yellow. It lies enveloped in a kind of membrane, in the floor of 

 the mouth or throat, being quite flat in the forward part, but 

 usually curving up so as to line the sides of the throat farther back, 

 and in some cases eventually forming almost a tube. The upper 



Fig. 3. — Portion of the radula of Melongena verpertilio, Lam., Ceylon, x 30. 



surface — i.e.^ the surface over which the food passes — is covered 

 with teeth of the most varied shape, size, number, and disposition, 

 which are almost invariably arranged in symmetrical rows. These 

 teeth are attached to the cartilage, on which they work by muscles, 

 which serve to erect or depress them ; probably also the radula, 



Fig, 4. — Portion of the radula of Ebiirna japonic a ^ Sovvb., China, x 30. 



as a whole can be given a forward or backward motion, so as to 

 rasp or card the substances which pass over it. 



The extreme importance of a study of the radula depends 

 upon the fact that in each species, and, a fortiori^ in each genus 



