SOFT-BODIED ANIMALS— THE MOLLUSKS 287 



5. What provision is made for distribution of young clams ? 



6. Why does the oyster have no foot? 



7. Tell how pearls are produced. 



8. Describe locomotion in the snail. 



9. What is the significance of the embryonic shell in the slug? 



10. What is the purpose of the pen and ink of the squid ? 



11. How does the octopus differ from the squid? 



12. Why is Chiton of importance in a study of the Mollusca? 



13. How is water drawn into the siphon of a clam? 



14. Name the mollusks that are important sources of human food. 



15. How is pearl formation stimulated artificially ? 



16. Describe the arrangement of the shell of the chambered nautilus. 



17. What is the significance of the similar embryos of Planar ia, Neanthes, and 

 Chiton ? 



