PHYLUM PROTOZOA 73 



the name contractile vacuole. If you have a favorable specimen, watch and 

 describe in your notes the behavior of the vacuole, and time the interval between 

 contractions. When the vacuole reappears after a contraction, is it the same 

 size as previously? Sometimes two or more vacuoles may be present, but they 

 generally coalesce into one later. What is the function of the contractile 

 vacuole (R)? 



b) The nucleus: This is a sharply outlined, finely granular body in the 

 neighborhood of the contractile vacuole, often in contact with it and of about the 

 same size as the fully expanded vacuole. Its granules, which are chromatin 

 granules, are much finer and more regularly distributed than those of the endo- 

 plasm. Determine the real shape of the nucleus by watching it as it rolls along 

 in the moving endoplasm. Is it spherical? Occasionally specimens are found 

 which have two nuclei. 



c) Food vacuoles: The endoplasm usually contains particles or masses of 

 digesting food, the larger of which may be inclosed in a drop of fluid and hence 

 are called food vacuoles. Find out in your text how the Amoeba digests food. 

 How does the process compare with that of the frog? 



Make an enlarged drawing of the Amoeba, and put into it all of the details 

 of structure described above. Indicate the granular appearance by stippling 

 with the pencil point. 



4. Activities. Can you observe any indications that the amoeba is irritable 

 and responds to the varying conditions of its environment? For instance, what 

 does it do when it comes in contact with an obstacle or when other animals 

 strike against it? If possible, observe the reaction to food material. How do 

 you suppose the amoeba distinguishes between food particles and other particles? 

 What does the amoeba do when it comes in contact with food material? Describe 

 in your notes and sketch this behavior, if you are so fortunate as to observe it. 



5. General considerations on the amoeba. Does the amoeba carry on all 

 the physiological processes that we found to occur in the frog? Does it have 

 any special organs for these processes? What are the significant differences and 

 resemblances between the amoeba and the frog? What does the frog gain by 

 its greater complexity of structure? To what stage in development of the frog 

 does the amoeba correspond? Give these questions careful thought and answer 

 specifically in your notes. 



C. PARAMECIUM 



The study of this animal is usually somewhat difficult owing to its swift 

 movements. In order, therefore, to obtain satisfactory results the student must 

 follow the directions very closely (Hegner, chap, v, pp. 59-79)- 



i. General form and movements. Mount a solid piece of scum and a drop 

 of water from the culture on a slide and examine under the low power without 

 a cover glass. A number of different organisms will probably be present and 



