CHAPTER IX. 



CV 



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 any- 

 where, is one of the most clas- 

 sic forms of uni-cellular life 

 that is made use of in the lab- 

 oratory. This single-celled 

 animal has all of the four char- 

 acteristics necessary for a liv- 

 ing being. It is found almost 

 anywhere but. it does not fol- 

 low that it is found every- 

 where. In fact, unless particu- 

 lar arrangements are made to 

 have the Amoebae ready at the 

 time they are wished for study, 

 the probabilities 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 ana- 

 tomy 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 granular cyto- 



plasm, known as the endosarc ( ). A contractile 



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

 mal opposite the part that is moved rnost frequently. There may be 

 Several food vacuoles, various foreign substances such as grains of sand, 

 and undigested particles (this 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 distinguishable 

 in living Amoebae. For this purpose animals are killed and stained, 

 mounted upon slides, and studied very carefully with the compound 

 microscope. 



The nucleus changes with the various movements of the animal, so 

 that it will not be found in the same location in all Amoebae studied. It 



Fig. 44. Amoeba Proteus. 



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

 mal that has swallowed a long filamentous plant ; C, 

 the animal in the state of division. 

 cv, contractile vacuole ; 

 ec, ectosarc ; 

 in, endosarc ; 



ex, remains of undigested food ; 

 p, protoplasm. (After Conn.) 



