218 



SNAILS AND SLUGS 



[CH. VII 



the external circular and internal longitudinal muscular 

 coats urges the food onwards. Further chemical changes 

 are effected in the food by the secretion of the digestive 



12 



13 8 



11 



Fig. 40. Inner view of right half of head of Helix, to show the 

 arrangement of the Kadula x 2. 



Mouth. 2. Horny jaw. 3. Eadula. 4. Cartilaginous piece 

 supporting radula. 5. Eadula sac from which radula grows. 



6. Muscle which retracts the buccal mass. 7. Intrinsic muscles 

 which rotate the radula. 8. Cerebral ganglion. 9. Pedal and 

 visceral ganglia. 10 (Esophagus. 11. Anterior tentacle. 



12. Eye tentacle. 13. Orifice of duct of salivary gland. 



14. Mucous gland which runs along foot and opens just under the 

 mouth . 



Fig. 41. A small portion of the radula of Helix. The central row 

 of teeth has been shaded. Magnified. (After Howes.) 



gland or " liver." Our knowledge of the action of this 

 gland is still incomplete. It is known that its secretion is 

 acid and contains both diastatic and peptic ferments and 



