Write a short account of the following:--

12. Oyster culture.

13. Typhoid-fever and oysters.

14. Clams, scallops, and other edible sh.e.l.lfish.

15. Pearls and pearl fisheries.

16. Fresh-water clams and the b.u.t.ton 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 cla.s.s, habitat, and some important fact about each of the following: Pectens; wing sh.e.l.ls; 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 sh.e.l.ls of protozoans composed?

2. How are the spicules formed in a simple sponge? What are gla.s.s 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 cuc.u.mber 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 sh.e.l.l in the case of crustaceans? What advantage in the arthropod type of exoskeleton?

7. Why are mollusks so commonly called "sh.e.l.lfish"? 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?

3. What is the explanation of the various forms of exoskeletons found?

4. Of what substances are exoskeletons composed?

#B. PROTECTIVE COLORATION#

#To show how Color may be Protective#

_Materials._

Specimens such as the Kny-Scheerer mimicry collections, diagrams, etc.

_Definitions._

_General protective resemblance_, the general resemblance between the color of an animal and its surroundings.

_Variable protective resemblance_, the changing of the color of an animal to correspond to the change in its background.

_Special protective resemblance_, the resemblance of an animal to some object found in its background in color and form.

_Mimicry_, the resemblance of an unprotected animal to a well-protected one.

_Warning colors_, bright colors which protect animals by causing other animals to avoid it.

_Questions._

1. Show how the transparent color of a paramecium, the green color of a cabbage worm, or the green color of a certain species of hydra may result in protecting an animal from its enemies. Mention as many other examples as you can.

2. What is gained by the ability of a squid to change its color? How is this change brought about?

3. Explain the protective coloration of the following: Dead-leaf b.u.t.terfly, walking stick, geometrid larva. Hunt up other examples.

4. Explain the protective coloration in the following: Hover flies, clear-winged moths, viceroy b.u.t.terflies.