_Suggested drawings._

a. At least one drawing of each clenterate you study.

Summary of the Comparative Study of Clenterates

1. How may polyps in colonial forms differ from polyps which live singly?

2. What variations in methods of reproduction are shown in this group?

3. Which of the polyps you have studied shows the greatest differentiation? In what ways?

4. What characteristic do you find common to all the clenterates you have studied?

Review and Library Exercise on Clenterates

1. What are the characteristics which distinguish clenterates?

2. Give the cla.s.ses of clenterates, with the characteristics and an example of each.

3. What enables a hydra to stick to a support by its foot?

4. What are the processes in a hydra by which food is captured, swallowed, and digested?

5. What is the chief fact of interest about Hydra viridis?

6. Why do hydras reproduce all summer by budding and in the late fall by eggs?

7. What change would have developed a hydra and its offspring into a plant-like colony instead of into a group of individuals?

8. Why are ctenoph.o.r.es more easily seen in the night than other clenterates are?

9. What relations may exist between hydroids and hydro-medusae?

10. What are the advantages of a sedentary life? Of a locomotory one?

11. What is meant by the expression "alternation of generations"?

Which animals are likely to develop alternation of generations, sedentary ones or locomotory ones? Why?

12. Give at least two differences between hydro-medusae and true jellyfishes.

13. In the a.s.sociation between a hydractinia colony and a hermit crab, what advantages are derived by the hydractinia? by the crab?

Define symbiosis. Give another ill.u.s.tration of it.

14. How are new coral colonies started? How are large colonies formed?

15. What are the conditions of life under which corals can grow vigorously?

16. Where are corals most abundant?

_Note._--Show by coloring the regions on a blank map of the world.

17. How may corals form a reef? Why do they, as a rule, form a reef instead of adding directly to the mainland?

18. Give Darwin's theory regarding the way a coral atoll may have been formed.

19. Where are fossil corals found in abundance? What does their presence prove?

20. What is polymorphism? Give an ill.u.s.tration. What may be a disadvantage of polymorphism? What may be an advantage?

21. In what ways is this group of economic importance?

4. A STUDY OF WORMS

_To show cells a.s.sociated even more closely than in clenterates, forming tissues and systems of organs._

#A STUDY OF EARTHWORMS#

The Living Earthworm

_Materials._

Living earthworms, some of which are left undisturbed from day to day, in damp earth with leaves of various plants scattered upon it.

_Definitions._

_Anterior end_, the head end, usually the leading end.

_Posterior end_, the end opposite the anterior end.

_Ventral surface_, the lower surface, usually the one which contains the mouth.

_Dorsal surface_, the one opposite the ventral surface.

_Somites_, the rings or segments of which some animal bodies are composed.

_Bilateral symmetry_, the symmetry usually shown by animals which have differentiated dorsal and ventral surfaces, and right and left sides. Animals which do not have such differentiated surfaces are usually _radially symmetrical_, but sometimes asymmetrical (without symmetry).

_Girdle_, the somewhat transparent band frequently found near the anterior end of an earthworm.