70 THE AMCEBA 



arrows on your figures to indicate the direction of flow within the 

 organism. 



Exercise 2. — General Structure. 



(c) Begin a drawing at least 10 cm. in diameter, and add the 

 various features as they are observed. The projections from the main 

 mass of the cell are the pseudopodia or "false feet." Observe their 

 function in locomotion and if possible in feeding. The outer, clear 

 region is the ectoplasm, and the inner granular portion of the animal 

 is the endoplasm. Some of the larger masses in the endoplasm are 

 within a clear drop of fluid. These spaces in the endoplasm, filled 

 with fluid surrounding bodies of various sorts, are the food vacuoles, 

 in which food is being digested. Can you identify within these vacu- 

 oles green plant cells or other organisms of the same kinds as found 

 living in the cultures with the amcebse? Such organisms can some- 

 times be observed within a vacuole and still moving. Examine the 

 other granules of the endoplasm, determining their size and shape. Is 



Fig. 35. — Reaction of an amoeba to contact with a surface. When the animal 

 is allowed to sink slowly through the water pseudopodia are extended in all 

 directions. If one of these comes in contact with the bottom or simihir 

 surface the cell responds in the manner shown, a, b, c, successive positions of 



same individual. 



(From II. S. Jennings, 1904, Carnegie Institution Pub. 16.) 



there a fixed boundary between ectoplasm and endoplasm? A single 

 large, clear vacuole can be identified as the contractile vacuole, if it 

 is seen to contract quickly and then to expand slowly. It is not eas- 

 ily recognized in the small specimens. This vacuole contains no 

 granules, only liquid collected from the endoplasm. The liquid is dis- 

 charged to the outside when the vacuole contracts. What is the func- 

 tion of the contractile vacuole? The nucleus is seen with difficulty in 

 small amoeba), but is recognizable in large ones as either oval or disk- 

 like in contour, finely granular, and about the diameter of the ex- 

 panded contractile vacuole. If the nucleus is not seen clearly in the 

 living amoeba, examine a demonstration of a stained and permanently 

 mounted specimen. 



