may be responsible for the production of 268,000,000 offspring in one month."

125. Study of amoeba (plural, amœbæ or amœbas). — (Optional laboratory study.)

A. Structure of amœba.

Examine a living amoeba or a stained specimen on a prepared slide. Use a low power of the compound microscope at first, and then as high a power as may be necessary. Make a sketch about three inches long to show the following:

1. An outline to show the shape of the animal, including any projections of the protoplasm, which are called pseudopods foot; hence, the name

(Greek pseudo false foot).

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false + pod

2. The main mass of the amoeba, clear and jellylike in a living amoeba, slightly stained in a mounted specimen, which is called the cell body.

3. A slightly denser part of the protoplasm in the living form or stained much darker in the preserved animal, the nucleus. 4. Particles of food or one-celled plants scattered through the cell body.

5. Label: false feet or pseudopods, nucleus, cell body, food particles.

6. If time allows, draw several different forms assumed by the specimen.

B. Locomotion.

In a living amoeba watch with the high power of the microscope the creeping movements, and the projections of the pseudopods.

1. Are the movements slow or rapid?

2. In your own words give a description of the locomotion of

the amo ba.

C. Excretion of liquid waste.

Look for a clear, roundish spot in the amoeba which at intervals disappears. This is the contractile vacuole. The liquid waste flows into this space and then the protoplasm pushes together and forces the waste out of the body.

1. Describe in your own words the appearance and action of the contractile vacuole.

2. Sketch the contractile vacuole in your drawing of the amoeba and label.

126. A comparison of paramecium and amœba. - - Both amoeba and paramecium are animals so small that they can barely be seen with the naked eye.

substance to flow out in many directions. These projections are known as pseudopods which mean false feet. By pushing out these pseudopods in front and pulling up its protoplasm from behind, the amoeba slowly flows from one part of the slide to another.

Unlike the paramecium an amoeba has no definite part of the body through which it takes in food. When the animal is feeding,

it slowly flows about the one-celled plant or animal and finally ingulfs it. The processes of digestion, assimilation, respiration, excretion, and reproduction (Fig. 121) are much the same in amoeba as in paramecium. Both these animals belong to a group of animals known as the Protozoa (Greek protos first or simplest + zoon = animal).

=

127. To show that the higher animals are composed of many cells. Laboratory study.

Frogs are continually shedding parts of their epidermis, and pieces of this thin membrane are likely to be seen clinging to a frog in an aquarium or floating in the water. Secure a piece of this membrane, spread it on a slide, add a drop of water and a cover glass, and examine with the low power of the microscope.

1. Describe the form and color of each cell. 2. In each cell notice a body, usually near the center and slightly more dense than the rest of the cell. This is the cell nucleus. (If the nucleus does not show clearly, add a drop of iodine to the membrane.) The rest of the cell is the cell body.

a. Name, now, two parts of a cell of the frog's epidermis.

b. State the form and position of the cell nucleus. 3. Make a drawing of three of the cells described above, each cell to be represented about an inch in diameter. Label cell body and cell nucleus.

4. (Optional.) Demonstrate by the use of prepared slides, pictures, or charts that the blood, intestine, and other organs of the body of a frog or other higher animal are composed of cells. Make a drawing of a single cell in each case.

128. A comparison of Protozoa and the higher animals. — Our study thus far has shown that all animals, including the Protozoa, perform the necessary functions of locomotion, food getting, assimilation, respiration, and reproduction. The adaptations for performing these functions, however, are very diverse.

All animals except the Protozoa consist of many cells and the various functions of the higher animals are performed by groups of cells known as organs. For example, certain combinations of cells carry on locomotion, others digestion, while still others are set apart for breathing. All these functions. are performed in a Protozoan by a single cell.

129. Economic importance of Protozoa. Most of the Protozoa serve as food for other animals that live in the water and these in turn are fed upon by fish, which are eaten by man. Thus the one-celled plants and animals are found to be an important food-basis for human beings.

Some of the Protozoa that live in the sea secrete tiny shells (Fig. 122), and when the animals die the shells drop to the bottom. As a result of heat, pressure, and other causes, this bottom ooze is gradually solidified to form chalky rocks, and in the upheavals that have taken place in ages past these rocks have been forced above sea level. The

chalk cliffs of Dover, England, were doubtless formed in this way.

While most of the Protozoa are harmless, there are a few

forms that have become parasitic in human beings. We have already discussed the single-celled animal that causes malaria and that is carried from one individual to another by the Anopheles mosquito (39). This parasite resembles an amoeba in form. Another form of Protozoan causes the terrible disease known as the sleeping sick

ness of tropical Africa. Many

biologists believe that yellow fever (41) is caused by a protozoan that is transmitted by the Stegomyia mosquito.