An example of Ciliophora is Paramecium caudatum (Rust, fig. 9-10; C & V fig. 4.19) - These free-living organisms almost always occur in fresh water containing decaying vegetation. They feed on bacteria.

(1) Living Organisms

Place a few drops of the culture on a slide and examine under low power. The large slipper-shaped organisms are paramecia. After you have studied the rapid swimming movements of these organisms, add a drop of methyl cellulose solution to the preparation and place a coverslip on top. The methyl cellulose is viscous and will slow their movements and, after a time, will give you quiet specimens. There is a depression on one side of the organism, the oral groove. Study an organism with the high dry objective. The body is covered with cilia. Are all cilia of equal length? The outer surface of the cell is fairly rigid and is composed of several layers of membrane, which along with other structures, make up the pellicle. Adjacent to the pellicle and extending into the endoplasm are numerous rod-like trichocysts. The endoplasm contains food vacuoles that originate from the end of the buccal cavity. Watch for a membrane-bound food vacuole form and release from the buccal cavity. At each end of the organism you can see a contractile vacuole. How often do they contract? Are they synchronous? Can you observe a connection between vacuoles and the surface of the organism? What is their function? Make a detailed drawing of Paramecium about five inches long.

(2) Discharge of Trichocysts

On another slide, place a drop of paramecia. Add a small drop of methyl green or nigrosin stain and add a coverslip. Find the tangled strands of discharged trichocysts. Although their actual role has not been definitively identified, they may serve as a defense mechanism. The discharged trichocysts are considerably longer than the cilia. This preparation should also show you the nuclei. One of the main characteristics of ciliates is the presence of dimorphic nuclei. Virtually all ciliated protozoa have two nuclei, a macronucleus, the source of RNA and the nucleus that carries out daily activities of the cell, and a micronucleus, the genetic nucleus involved in meiosis and sexual reproduction (conjugation in the ciliated protozoa). See your textbook for nuclear events associated with sex in ciliated protozoa. On your stained slide you should see the macronucleus. Add its shape and location to the diagram you have already made. The micronucleus may be more difficult to see. In Paramecium it is located adjacent to the macronucleus.

(3) Silver-stained Paramecia

Silver stains are a method of choice demonstrating details of the pellicle and cilia and basal bodies. The slides provided have been prepared to show basal bodies, contractile vacuole pores and the cell anus of Paramecium, the cytoproct. Examine the rows of basal bodies and see the specialized groups of cilia in the buccal cavity (these usually are tightly spaced, and generally stain lighter by this method). In the right orientation, you should locate the contractile vacuole pores, which stain as round discs about the size of five-ten basal bodies. How many of them are there? Are there different numbers associated with anterior and posterior contractile vacuoles? The cytoproct stains as a faint line that is to be found just posterior to the oral groove and on the same side of the organism. How long is it?

(4) Reproduction

Paramecium, like most other protozoa, is able to reproduce by dividing into two equal daughter cells by a process of binary fission. Examine the prepared slides showing binary fission in Paramecium. Note that division occurs in a transverse plane. This is a characteristic of the ciliated protozoa and distinguishes them from flagellated protozoa, which divide alone the longitudinal plane. Paramecium also reproduces sexually by the process of conjugation. During conjugation two organisms come together, temporarily fuse along their oral areas, and exchange micronuclei. Then the cells separate, reorganize their nuclear material, replace their macronuclei with the newly organized genetic material and subsequently undergo further division.