74 THE PARAMECIUM 



Exercise 2. — General Structure. 



(c) Put a small number of absorbent cotton fibers, or of the fibers 

 frayed from a piece of lens paper, on the. drop containing the para- 

 mecia; or add a drop of thick tragacanth mixture to the drop of cul- 

 ture; then add a cover glass. The fibers will form pens enclosing the 

 animals without crushing them or the tragacanth will prevent rapid 

 motion, thus enabling you to observe the specimens under the high- 

 power objective. Determine the shape and extent of the buccal groove, 

 which extends backward from the anterior end on one side of the cell. 

 How does it end posteriorly? The function of this blind pocket, the 

 gullet, will be studied later. Observe the cilia on the surface of the 

 cell. Are they the same length on all regions? Are their movements 

 coordinated during locomotion? A clear vesicle near each end will be 

 seen to enlarge slowly and suddenly disappear. These are the con- 

 tractile vacuoles. Their activities will be observed more closely later. 

 Numerous food vacuoles can be seen scattered throughout the cell; 

 they contain various materials. Note that the cell consists of an outer 

 layer of clear ectoplasm surrounded by a cuticle which appears as a 

 firm line on animals that are compressed by the cover glass. The 

 inner granular portion of the cell surrounding the food vacuoles is 

 the endoplasm. Do you observe motion of the granules and food 

 vacuoles? 



(d) Draw off the water from the edge of the cover glass with filter 

 paper until the animals are almost crushed. Look along the margin 

 of the cell for rodlike bodies in the ectoplasm, the undischarged tricho- 

 cysts. Draw off the water until the animal is crushed and the endo- 

 plasm flows out. Examine this carefully with the highest magnifica- 

 tion to be obtained with your microscope. Examine the cuticle care- 

 fully. Can you see markings on its surface? Make a figure, 10 cm. 

 long, with the buccal groove uppermost, and show the structural fea- 

 tures observed so far. 



(e) Make a fresh mount of the culture only and add a drop of 

 methyl green. Determine the shape of the macronucleus. What is the 

 difference in the reaction of the nuclear material and the cytoplasm 

 to the stain? Does this indicate anything regarding their chemical or 

 physical composition? Such crude staining methods do not ordinarily 

 demonstrate the smaller micronucleus which lies in a depression in the 

 macronucleus. Examine a demonstration showing the micronucleus 

 and add these two structures to your previous drawing. 



(f) Examine the margin of specimens stained with methyl green, 

 iodine, or fountain-pen ink and look for heavy rodlike processes, much 



