CHAPTER III 



UNICELLULAR ORGANISMS 



IN order to become familiar with the general properties of 

 living things, we will study the structure and functions of some 

 of the simplest organisms. Those that are studied in this chap- 

 ter are all microscopic, and belong to the group of unicellular 

 organisms sometimes called animalculae. 



ANIMALS 



The first organisms to be studied are undoubtedly to be 



regarded as animals. 



AM(EBA 



Size and Shape. The Amoeba (Gr. amoibos changing) is 

 a microscopic animal found both in fresh and salt water. The 

 most common species averages about 1/100 of an inch in diam- 

 eter, but the size varies in different species. With perseverance 

 they may be discovered in nearly all bodies of water where there 

 is mud and slime. One of the best methods of procuring them 

 for study is to collect water plants (Ceratophyllum) or even pond- 

 lily leaves, and to place them in dishes of water until they decay. 

 After a couple of weeks or so a brown scum appears and an 

 examination of this scum usually shows Amoebce in abundance. 



Under the microscope the Amoeba is seen to be a single cell 

 without definite form, the same animal undergoing constant 

 changes in outline. Lobes are thrust out first in one direction 

 and then in another (Fig. 19), and as soon as one lobe is protruded 

 the contents of the body begin to flow into it and may continue 

 to flow until the whole body substance has passed into the lobe, 

 other lobes being formed in the meantime. By a continual pro- 

 trusion of such lobes and the flowing of the body into them, the 

 Amoeba has a slow motion. These lobes are thus used as organs 

 of locomotion and are called pseudopodia (Gr. pseudos = false -f 

 pous = foot). 



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