76 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



In favorable cases you may observe minute food particles shooting down the 

 gullet and collecting into balls in its inner rounded end. Note the great activity 

 of the cilia in the gullet, where they are fused into a vibrating membrane, known 

 as the undulating membrane. The oral groove, mouth, gullet, and undulating 

 membrane are the food-catching apparatus of the Paramecium. Near the gullet 

 is a region inappropriately named the anus, where undigested food material is 

 extruded. It can be seen only when material is passing out through it. (The 

 terms "mouth," " pharynx," "anus," etc., should not have been applied to the 

 Paramecium as they do not in the least correspond to the structures so named 

 in the frog, except from the point of view of their function.) Enter the above- 

 mentioned details on your drawing. 



d] Contractile vacuoles: Observe a circular clear spot near each end of the 

 animal. These are the contractile vacuoles. They are located between the 

 ectosarc and the endosarc but firmly attached to the former. Are they on the 

 ventral or dorsal side? Watch the contraction and note the radiating canals 

 which appear like the petals of a flower around the point where the vacuole has 

 disappeared. What is the average time between successive contractions of a 

 vacuole? How does this compare with the contraction interval of the vacuole 

 of Amoeba^ The anterior vacuole of Paramecium generally contracts more 

 frequently than the posterior one. (Note that the vacuoles may cease to con- 

 tract or may contract very slowly in formalized specimens, and become very 

 large and abnormal in behavior in flattened specimens.) Enter vacuoles and 

 canals on your drawing. 



e) Nuclei: Paramecium and its relatives have two nuclei, a large meganucleus 

 (also called macronucleus) and a small micronudeus. They cannot be seen in 

 normal animals, but the meganucleus can usually be recognized as a central 

 large irregular mass in flattened and formalized individuals. Study the nuclei 

 in the stained slides of Paramecium which are in your box. The meganucleus 

 is a large-lobed and folded mass in or near the center, and the micronucleus is a 

 small spherical body lying in a concave depression of the meganucleus. Put 

 the nuclei in your drawing in their proper places. 



3. Experiments on Paramecium 



a) Formation and course of food vacuoles: Start this experiment at the begin- 

 ning of the laboratory period, as it requires some time for completion. It need 

 not be watched continuously and the other experiments may be performed during 

 the progress of this one. Mount some Paramecia with a piece of scum, add a 

 drop of India ink suspension, and cover. This experiment can be carried out 

 only on normal active animals, and the observations should be made on animals 

 which are resting about the piece of scum. Do not let your preparation become 

 dry. Find a quiet individual, and note that the particles of carbon are swept 

 rapidly down the gullet to its rounded termination where they collect into whirling 

 spherical masses. Observe that from time to time one of these masses breaks 



