4. Make cross-sectional diagrams to show the arrangement of parts in a clam: (a) in the region of the umbone; (b) in the region just in front of the posterior muscle; (c) in the region of the anterior muscle. 5. Describe the various types of eyes found in mollusks, and their location. 6. Describe the tongue or lingual ribbon of the snail, and its use. 7. What is the operculum of snails? its use? _Physiology._ 8. Describe the circulation of water through the siphons and mantle cavity of a clam. How is it caused? What three uses has it? 9. What are the principal facts about the development of fresh-water clams? 10. Describe the circulation of blood in a clam. 11. What various methods of locomotion are found among mollusca? _Economics._ Write a short account of the following:-- 12. Oyster culture. 13. Typhoid-fever and oysters. 14. Clams, scallops, and other edible shellfish. 15. Pearls and pearl fisheries. 16. Fresh-water clams and the button industry. 17. Sepia, Tyrian dye, etc. 18. Harmful and useful mollusks. 19. The work of U. S. Fish Commission in propagating clams. _Natural history._ 20. Give the class, habitat, and some important fact about each of the following: Pectens; wing shells; Tridacna gigas; abalones; limpets; oyster drill; periwinkle; mussel; cuttle fish; octopus; nautilus; argonaut. 6. A COMPARATIVE STUDY OF EXOSKELETONS _Materials._ Charts, specimens, etc. Since this is partly a review exercise, your notes and drawings of invertebrates should be at hand. _Definitions._ _Exoskeleton_, a protective covering developed on the outside of an animal. _Questions._ 1. What are foraminifera; radiolaria? How do they differ from other protozoans? Of what two substances are the shells of protozoans composed? 2. How are the spicules formed in a simple sponge? What are glass sponges? Give reasons why the skeletons of sponges may or may not be considered exoskeletons? 3. What are stone corals? What is the relation of the coral polyp to the skeleton? What is the appearance of the coral when expanded as compared with its appearance when contracted? Of what substance is the coral composed? 4. Describe the exoskeleton of a starfish. Contrast the exoskeleton of the sea urchin and the starfish. Why does a sea cucumber need no well-developed exoskeleton? 5. What structure in an earthworm may be considered an exoskeleton? What other types of exoskeletons are found in segmented worms? 6. Of what substance is the exoskeleton of arthropods composed? What additional substance is found deposited in the shell in the case of crustaceans? What advantage in the arthropod type of exoskeleton? 7. Why are mollusks so commonly called "shellfish"? What advantage in the mollusk type of skeleton? What disadvantages? _Summary._ 1. What type of exoskeleton is common among invertebrates? 2. What are the general purposes of exoskeletons?