AMCEBA, PARAMCECIUM AND VORTICELLA 39 



which shows no pulsations. This is the nucleus, a very com- 

 plex little structure of great importance in the make-up of 

 A mceba. 



Note that Amceba has no mouth or alimentary canal; no 

 nostrils or lungs, no heart or blood-vessels, no muscles, no 

 glands. It is an animal body not made up of numerous dis- 

 tinct organs and diverse tissues. Its whole body is a minute 

 speck of protoplasm, and forms a single animal cell. But it 

 takes in food, it moves, it excretes waste matter from the 

 body, is sensitive to the touch of surrounding objects, and, 

 as we may be able to see, it can reproduce itself, i.e., 

 produce new Amoeba. Amoeba is one of the simplest living 

 animals. 



It is only rarely that we can find an Amoeba actually repro- 

 ducing. The process, in its gross features, is very simple. 

 First the Amoeba draws in all of its pseudopodia and remains 

 dormant for a time. Next, certain changes take place in the 

 nucleus, which divides into equal portions, one part with- 

 drawing to one end of the protoplasmic body, the other to 

 the opposite end. Soon the body protoplasm itself begins 

 to divide into two parts, each part collecting about its own 

 half of the nucleus. Finally the two halves pull entirely 

 away from each other and form two new Amoeba, each like 

 the original, but only half as large. This is the simplest kind 

 of reproduction found among animals. 



Amoeba continue to live and multiply as long as the con- 

 ditions surrounding them are favorable. But when the pond 

 dries up the Amceba 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 the pro- 

 toplasm secretes a horny capsule about itself. It is now 

 protected from dry weather and can be blown by the winds 

 from place to place until the rains begin, when it expands, 

 throws off the capsule and commences active life again in 

 some new pond. 



