How To Study Living Animals


2. A STUDY OF SPONGES

To show how cells loosely associated 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 herunterladen. For these reasons the material for this study is very meager, except at the seashore, 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 herunterladen.

Central cavity,

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

Canals,

channels through the body walls of sponges.

Inhalent pores,

the outer ends of the canals.

Ostia,

the inner ends of the canals.

Osculum,

the large opening of the central cavity, at the distal end of the sponge microsoft office kostenlos downloaden vollversion deutsch chip.

Spicules,

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

Fibers,

flexible threads of horny material found in the walls of many sponges.

Endoderm cells,

cells lining the canals. 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 canals 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, canals, 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 amœboid 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.

1. What is the shape of a simple sponge? What enables a mass of cells to retain such a definite shape?

2. What seems to be the composition of the skeletons? Why is one type of skeleton rigid and the other elastic?

3. Since sponges are attached for most of their lives to stationary objects, suggest means for obtaining food and oxygen, and for getting rid of waste matter.

4. Although individual cells are sensitive, a sponge as a whole is not. What connection has this fact with the fact that sponges are stationary?

5. Compare simple and complex sponges.

Suggested drawings.

a. A view of a simple sponge. Label everything shown.

b. A diagram of a simple sponge split in halves. Show by arrows the path followed by the water as it passes through the sponge.

c. A few spicules.

d. A few fibers.

Summary of Important Points in the Study of Sponges

1. What are two functions of the spicules or fibers?

2. What are at least two of the functions of the endoderm cells?

3. What can you suggest as functions for the ectoderm cells?

4. In what cases do cells show “team work” in accomplishing an object?

5. What degree of specialization is indicated by the fact that the cells may exchange positions and functions?

6. What work can any single cell of a sponge do? Compare the work done by such a cell with that done by a paramecium.

7. What work can a whole sponge do? Compare that with the work done by a paramecium.