Metodical appointments to realizing task:
Place a drop of the culture on a slide, cover, and examine with the low power.
- In an animal not closely confined note the shape and movements. Is it possible to distinguish an anterior and a posterior end? A forward and backward movement? Is one side of the animal kept constantly uppermost ? Is there a dorsal and ventral surface? Do the animals change their shape either permanently or temporarily? Individuals tend to collect about air-bubbles and at the edge of the cover-glass. Why ? Indicate by a sketch all the points which can be determined with the low power.
- Draw off all superfluous water by means of filter-paper, add a trace of powdered carmine, and then find a specimen which is narrowly confined and examine it with the high power. The particles of carmine are taken into the body. Determine how and where. Note that the carmine collects in gastric vacuoles. What do you think is probably the nature of the fluid in the vacuoles? In watching them do you notice any definite movement of the protoplasm? Try to see the undigested material ejected.
- Determine the arrangement of the cilia, and the nature of their motion. Is there a reversal of the direction of the stroke.
- Observe the contractile vacuoles. How many are there? Is their position constant? What is their action? In coinpressed specimens the contractile vacuoles and their reservoirs are usually conspicuous. Note the order of appearance and disappearance of the vacuoles and reservoirs.
- Focus carefully on the margin of the body and nole a very thin outer cuticle. A thick layer, the ectoplasm, devoid of granules but containing radially arranged, minute, oval bodies, the trichocysts, is just internal to the cuticle. The inner mass of protoplasm, containing the contractile and gastric vacuoles, and small granules, is the endoplasm.
- If possible distinguish the clear, centrally located nucleus (macronucleus). Make a sketch showing all of the above points.
- Kill the animal by running a drop of methyl-green under the cover-glass. What happens to the cilia? To the trichocysts? Sketch the trichocysts with the threads protruded, and also note and sketch the macronucleus and the micronucleus.
- Observe, if possible, animals dividing and conjugating.
- Study demonstrations of permanently stained specimens for finer structure.