MOLLUSC A 



199 



The mouth leads into the cavity of the buccal mass, this 

 is partially obliterated by the developement of a large ventral 



Fig. 119. — Side view of anterior end of Limpet, 

 Patella milgata. Part of the mantle is cut 

 away to show the contents of the pallial cham- 

 ber. After Lankester — Zoological Articles re - 

 printed from the Encyclopcedia Britannica. 



5. Small nephridium. 



6. Large nephridium, 



7. External opening of small ne- 



phridium. 



8. External opening of large ne- 



phridium. 



9. Anus. 

 10. Rudimentary otenidium. 



Head. 



2. Tentacle. 



3. Mantle skirt. 



4. Muscles forming root of foot, and 



adherent to the shell. 



11. Pericardium.' 



mass, over which the tooth -ribbon or radula works. The 

 ventral mass contains certain cartilaginous nodules, and is very 



Fig. 120. — Vertical section through the neck of Patella mtlgaia. 



After R. J. Harvey Gibson. 



1. Mouth. 6. Anterior cartilage. 



2. Buccal cavity. 7. Oesophagus. 



3. Palatal tooth. 8. Radula sac. 

 i. :^adula. 9. Foot. 



5. Odontophore. 



muscular. The radula, which runs over it, is continued into a 

 sac, from the blind end of which it grows (Fig. 120). The radula 



