A STUDY OF AMCEBA 27 



these changes they effect a slow, flowing movement. Small 

 unequal projections, called pseudopodia, stretch out from various 

 parts of the body. At first these are formed only by the 

 ectosarc, but as they grow longer and larger the endosarc flows 

 out into some while others are withdrawn and new ones are 

 thrown out. The outline of the body thus continually changes. 

 As the animals move slowly about they come in contact with 

 other minute animals or plants around which the pseudopodia 

 flow and these organisms, which the Amceba uses for food, 

 are thus taken directly into the body. Any particles of food 

 or other substances which are taken into the body and not 

 digested pass out just as they entered, that is, the Amoeba 

 flows away and leaves them, much as a drop of oil that sur- 

 rounded a particle of sand might flow away and leave the 

 sand. 



The oxygen that the Amoebae need is absorbed from the 

 surrounding water. Some of the waste excretions of the body 

 are absorbed directly by the water, others are forced oat by 

 the contractile vacuole. 



Thus we see that while the Amceba has no mouth or ali- 

 mentary canal, no lungs or heart, muscles, glands or any of the 

 special organs and tissues that go to make up the higher ani- 

 mals, this minute speck of living substance moves, feeds, 

 respires, excretes and does all the essential things that the more 

 complex organisms do. As the Amceba feeds it grows until 

 it reaches a more or less definite size, then certain changes 

 take place in the nucleus which soon divides into two equal 

 portions, one portion withdrawing to one part of the body and 

 the other part to the opposite end. Then the substance 

 around the nuclei begins to divide, a portion collecting around 

 each of these nuclei. Finally the two halves pull entirely 

 away from each other and thus two new Amoebae are formed, 

 each like the original, but only half as large. 



Amoebas continue to live and multiply as long as the condi- 

 tions surrounding them are favorable. But when the pond 

 dries up the Amoebae in it would be exterminated were it not 

 for a careful provision of nature. When the pond begins to 

 dry up each Amceba contracts its pseudopodia and secretes 



