CHAPTER IX 



THE PROTOZOA 

 AMOEBA 



JUST as the frog is easily obtainable and most frequently studied in 

 the laboratory, so the Amoeba (Fig. 44), because it may be found 

 anywhere, is one of the classic forms of uni-cellular life that is made 

 use of in the laboratory. This single-celled animal has the four char- 

 acteristics necessary for a liv- 

 ing being. It is found almost 

 anywhere, but not necessarily 

 everywhere. In fact, unless 

 particular arrangements are 

 made to have the Amoebae 

 ready at the time they are 

 wished for study, the probabil- 

 ities are that they will not be 

 found where one is looking for 

 them. 



Just as with the frog, so 

 with a single-celled animal, we 

 attempt first to study its 

 anatomy or morphology. We 

 want to ascertain what seeable 

 parts go to make up this tiny 

 animal. We find in it all the 

 constituents of a cell and all 

 the needed characteristics to make an organism. 



There is an outer colorless layer of clear cytoplasm, called the ecto- 

 sarc ( ), then a large central mass of grandular cyto- 



plasm, known as the endosarc ( ). A contractile 



or pulsating vacuole will usually be found lying in that part of the 

 animal opposite the part which is moved most frequently. There may 

 be several food vacuoles, various foreign substances such as grains of 

 sand, and undigested particles (these latter depending, of course, upon 

 whether the animal is studied immediately after it has been feeding 

 extensively). Then there is also some material which has been digested 

 and is ready for excretion, and a nucleus. The nucleus is not easily dis- 

 tinguishable in living Amoebae. For this purpose animals are killed and 

 stained, mounted upon slides, and studied very carefully with the com- 

 pound microscope. 



Iff 



Fig. 44. Amoeba Proteus. 



A, the animal in its natural condition; B, an ani- 

 mal that has ingested a long filamentous plant; C, 

 the animal in the state of division. 

 cv, contractile vacuole; 

 ec, ectosarc; 

 en, endosarc; 



ex, remains of undigested food; 

 p, protoplasm. (After Conn.) 



