A Guide for the Study of Animals Part 15

_Food b.a.l.l.s_, bits of food inside the cells of many one-celled animals, usually showing through the walls.

_Food vacuole_, a small drop of water containing digestive material and a food ball.

_Contracting_ or _pulsating vacuoles_, small, clear spots in the cell, filled with water. In the living cell these disappear at intervals and then appear again.

_Oral groove_, a funnel-shaped groove in one side of some one-celled animals, conducting food to the mouth. In paramecium it often shows as an oblique line when the animal rolls.

_Gullet_, the inner end of the oral groove.

_Cilia_, numerous minute, vibrating, protoplasmic hairs on the surface of many cells.

_Respiration_, the pa.s.sage of oxygen into the tissues of a living organism and of carbon dioxide out of them. These gases can pa.s.s through any thin, moist, organic membrane. When such a membrane separates two fluids which differ in the amount of oxygen they contain, oxygen pa.s.ses to the fluid containing the smaller amount.[2]

The same is true of carbon dioxide. Respiration is believed to occur in all living organisms.

[2] This pa.s.sage of fluids through membranes is known as _osmosis_.

_Digestion_, the process of making food materials soluble, so that they can pa.s.s through membranes and be used to build up protoplasm. A few forms of cells are able to take in solid food and digest it in their protoplasm, but most cells can admit only fluid food.

_Fission_, a method of reproduction used in all cells, by which a cell divides itself into two, usually through the center. In some one-celled animals this may be preceded by _conjugation_, when two animals unite temporarily and exchange nuclear substance; or in some forms two cells may fuse and the resulting cell may divide. _Budding_ is a form of fission in which a small projection is formed on the parent cell and then cut off, making a new individual.

_Protozoa_ (first animals), animals of one cell, existing alone or in loose colonies.

_Observations._

1. Examine a single cell, stained to show structure. Identify the nucleus, cytoplasm, and, if present, the nucleolus or the micronucleus, and the cell wall. Draw to show the form of the cell and the details of its structure. Label all details.

2. Examine some stained paramecia. Select a typical one and identify in it nucleus, micronucleus, cytoplasm, and cell wall or cell membrane. You may also be able to see vacuoles, looking like holes in the stained protoplasm. Give reasons for considering this animal to be a single cell. Draw one, to show its cellular structure. Label all details.

3. Clean a slide and cover gla.s.s, place a drop of water containing living paramecia on the slide, cover it, and examine. What structures do you see which you saw in the stained paramecia? What structures do not show? Identify any new structures you may observe. Identify also the leading end and the side containing the oral groove.

4. Describe the shape of the animal.

What is the actual length of the animal?

5. After watching the animal for some time, describe the path followed by a given specimen as it crosses the field of the microscope. What reason can you see, if any, why this paramecium is moving? What external factors, if any, seem to determine the path it follows?

6. How rapidly do paramecia really move? What structures do they use in locomotion?

How do they manage to move in one direction, instead of alternately backward and forward? How do they manage to move in a straight line, though their bodies are not symmetrical?

7. What is the food of the paramecia? How do they find it? Find a specimen at rest and watch the oral groove. Suggest a method by which food may be collected into it. If possible, note the process of swallowing, and the resulting food ball.

_Note._--If powdered carmine be placed in the water with some paramecia, it can be seen in the food b.a.l.l.s a half hour or so later.

8. Where are the food b.a.l.l.s located? Watch them in an individual until you notice their motion. Where are the larger food b.a.l.l.s? the smaller ones? a.s.suming them to have been of approximately equal sizes when they were taken in, how can you account for differences now?

9. Where are the contracting vacuoles? How many are there? How often does one contract?

What is their function?

10. As you have been studying paramecia, to what external influences (as contact, heat, light, etc.) have you seen them respond? How do they show it when they do respond? Is such a response an advantage to them or not? What would be the result if they were not able to detect changes in their surroundings?

11. Where does respiration occur in paramecia? Where do they obtain their supply of oxygen?

12. Among the paramecia you are studying you usually find at least one in the process of fission. Watch it until the halves separate, if you can. Compare the halves. Do they rank as parent and offspring? If so, which is which? If not, which are they, parent or offspring?

13. If you happen to find a pair conjugating, notice the process, as far as you can, in the living animals.

_Suggested drawings._

a. A drawing to show all the details seen in the living paramecium.

b. A diagram to show the path followed by a paramecium to get around some obstacle.

c. Drawings to show that paramecia are constant in shape and yet flexible.

d. A drawing to show at least one stage in fission. This may be from a permanent preparation.

e. A drawing to show paramecia conjugating. This also may be from a permanent preparation.

f. Instead of all these separate drawings they may be combined into one. Represent the field of the microscope, and in it draw all necessary figures, to show the facts called for in the first five drawings and any other facts you have observed about living protozoa.

Make the whole drawing to scale.

Summary of Important Points in the Study of Paramecia

1. Look back over your study of paramecia and list the different kinds of work you saw paramecia doing; also the kinds of work you infer they can do. What organs have they to use? When there is no organ to do a given thing, _e.g._ to digest food, how is the work done?

2. What conditions are favorable to paramecia? Why are they so numerous under favorable conditions?

3. What would you call a successful animal? Are paramecia successful?

Give reasons why they are or are not.

Comparative Study of Protozoa

To enlarge your idea of what a cell can do, spend as much more time on the one-celled animals as your course will permit. Any stagnant water may furnish several kinds. By means of reference books, identify as many as you can. In each case notice:--

1. Its size, shape and general appearance, comparing and contrasting it with paramecium.

2. Its usual surroundings, _i.e._ the conditions it has to meet.

3. The means it has of finding out facts about its surroundings.

4. The means it has of adjusting itself to its surroundings. For example, is it stationary? If so, what does it do when conditions change? Is it locomotory? If so, how effective is its locomotion?