A Guide for the Study of Animals Part 16

5. What is its food? How does it find food?

6. Can it do as many kinds of work as paramecium can? Can it do any that paramecium cannot do? If so, what?

Review and Library Questions on Protozoa

1. What are the characteristics which distinguish protozoa from other animals?

2. What are the cla.s.ses of protozoa? Characteristics of each cla.s.s?

3. What is digestion? Where does it take place in the protozoa?

4. What results from the fact that the amba has no cell wall? (Give at least two points.)

5. In what ways are paramecia more specialized than amba are? How does their greater specialization show in their work?

6. What different methods of locomotion are shown among protozoa? By what means is locomotion accomplished in each case?

7. What is encysting? Name some protozoa which encyst. How long may an encysted animal live? When do they encyst? Why?

8. Give methods of reproduction among protozoa. Which method is fitted for rapid multiplication, for withstanding drouth; for renewing vitality?

9. Many scientists speak of protozoa as immortal. What argument is there to support such a statement?

10. Why are no protozoa large animals? Give at least two reasons.

11. Why are protozoa so numerous? Why more numerous in stagnant water?

12. Where are protozoa found?

13. Why are protozoa so widely distributed?

14. Write the probable history of a piece of chalk.

15. What connection is there between protozoa and some polishing powders?

16. Where in the human body are malarial protozoa found? How are they transferred from one human being to another? Why is there likely to be more malaria in newly settled regions than in older ones? If you were obliged to spend some time in a region where malaria existed, what precautions would you take?

17. Name other diseases caused by protozoa. How are they fought?

18. What beneficial effect have some protozoa upon the water of stagnant ponds and ditches? How may some forms injure water for household purposes?

19. Give at least three reasons for thinking that protozoa are the most ancient animals.

20. Why are protozoa of great importance to the world?

2. A STUDY OF SPONGES

_To show how cells loosely a.s.sociated may work together_.

_Materials._

The simplest of the many-celled animals are the sponges, which, with one exception, are salt-water forms. That one, the spongilla, is not easily found and is very difficult to maintain in the laboratory. For these reasons the material for this study is very meager, except at the seash.o.r.e, and much of the work must be done from diagrams and reference books. Small simple preserved sponges and complex toilet sponge skeletons will also be used.

_Definitions._

_Body wall_, the outer wall in bodies of the many-celled animals.

_Central cavity_, the cavity surrounded by the body wall in the simpler many-celled animals, as in the sponges.

_Ca.n.a.ls_, channels through the body walls of sponges.

_Inhalent pores_, the outer ends of the ca.n.a.ls.

_Ostia_, the inner ends of the ca.n.a.ls.

_Osculum_, the large opening of the central cavity, at the distal end of the sponge.

_Spicules_, tiny needles of mineral substance found in the walls of many sponges.

_Fibers_, flexible threads of h.o.r.n.y material found in the walls of many sponges.

_Endoderm cells_, cells lining the ca.n.a.ls. They have cilia or flagella (projections larger than cilia).

_Ectoderm cells_, cells covering the outside of sponges and some other animals. In sponges it is believed that endoderm and ectoderm cells are able to exchange positions and functions.

_Mesoglea_, a jelly-like layer between the endoderm and ectoderm layers. In the sponges this contains many wandering cells, probably from the other layers.

_Porifera_ (pore bearers), animals with many more or less independent cells, supported by solid skeletal parts and penetrated by a system of ca.n.a.ls which open on the surface as pores.

_Directions._

Study a simple sponge to see the shape, size, and point of attachment. Identify the osculum. In a diagram of a long section of a simple sponge identify the central cavity, body walls, ca.n.a.ls, inhalent pores, ostia, and osculum. In a simple sponge cut like the diagram identify the same structures. Do the same for the toilet sponge.

Study a diagram of a portion of the body wall, considerably enlarged.

Identify the endoderm and ectoderm cells, the spicules or fibers, and, among the spicules or fibers, irregular amboid cells, sometimes called mesoderm cells.

Examine a fragment or section of each kind of sponge under the microscope. Notice the arrangement, shape, and length of the spicules and of the fibers.

Test both kinds of sponges by dropping a bit of each into weak acid, and noting the results. Also burn a bit of each and notice the odor.

_Questions._