Protozoa. 165 



1. The shape, oval or elliptical, often decidedly slipper-shaped. 

 It further resembles a slipper in being somewhat flattened. 



2. Structure. The clearer, firmer, outer layer is the ectosarc. 

 The more jellylike inner part is the endosarc. Covering the ecto- 

 sarc is a thin, transparent layer, the cuticle. Extending from the 

 ectosarc through the cuticle are many fine, hairlike projections, the 

 cilia. Near the center is a large, ovoid body, the macronucleus. 

 Beside it is the much smaller micronucleus. These nuclei are 

 hard to see. Place a little dilute acetic acid on the slide close 

 to the cover slip to bring out the two nuclei. 



3. Locomotion. The paramecium swims by means of the 

 vibrations of the cilia. Does it swim with the same end always 

 foremost ? Does it change its shape ? Watch it when trying to 

 pass into a narrow opening. Are the cilia of the same size all 

 over the body ? Place a drop of iodine solution on the slide at 

 the edge of the cover slip. The cilia, thus stained, show 

 better. 



4. Feeding. Along one of the flattened surfaces find a groove, 

 the oral groove. Note the cilia lining this groove. Observe that, 

 near the center of the body, the oral groove becomes a tube 

 dipping into the body. The tube is the gullet, and its be- 

 ginning is the mouth. Sift finely powdered carmine or indigo 

 into the water, and watch to see the particles swept into the 

 gullet by the action of the cilia. The masses of particles that 

 accumulate at the end of the gullet become separated from the 

 gullet, and as distinct masses in the body are called food vacuoles. 

 Do the food vacuoles remain in the same place ? Or do they 

 move about ? Do they move in any regular order ? Can you 

 find a place where the residue is expelled from the body ? 



5. Pulsating Vacuoles. About one third of the way from each 

 end, look for a clear space, which contracts and disappears, and 

 then reappears ; these are the pulsating vacuoles, or contractile 

 vesicles. How often do they pulsate ? Which takes more time, 

 contraction or dilation ? Look closely for radiating canals after 



