PROTOZOA 



181 



Reproduction of Paramcecium. — Somctimos a paramoecium may be 



found in the act of dividing by the process known as fission, to form two 



new cells, each of which contains half of the oiigi- 

 nal cell. This is a method of asexual reproduc- 

 tion. 



Frequently another method of reproduction may 

 be observed. This is called conjugation and some- 

 what resembles the same process in the thallo- 

 phytes. Two cells of equal size attach themselves 

 as shown below, complicated changes take place in 

 the nuclei of the two cells thus united, and after a 

 short period of rest the 

 two cells separate as two 

 new individuals. These 

 new animals appear to be 

 rejuvenated as a result of 



conjugation, and may continue to reproduce asexU' 



ally by fission for a long period of time. Even- 



ually, howeve--, it seems necessary for the cells to 



conjugate in order to continue their existence. This 



stage of conjugation we believe in the plants to be 



a sexual stage. There seems every reason to 



believe that it is a like stage in the life history of 



the paramoecium. 



NAC. 

 M/C. 



Paramoecium dividing by 

 fission. Greatly magni- 

 fied. M, mouth; MAC, 

 macronucleus; MIC, 

 micronucleus. (After 

 Sedgwick and Wilson.) 



maQ 



Paramoecium conjugating. 

 Greatly magnifietl. M, 

 mouth ; Mic , micro- 

 nucleus; Mac, macro- 

 nucleus; CF., contrac- 

 tile vacuole. (.\fter 

 Sedgwick and Wilson.) 



Amoeba. — In order to understand more fully the life of a 

 simple bit of protoplasm, let us take up the study of the amoeba, 

 a type of the simplest form of life known, either plant or animal. 

 Amoeba may be obtained from the dead leaves in the bottom 

 of small pools, from the same source in fresh-water aquaria, 

 from the roots of duckweed or other small water plants, or from 

 green algae growing in quiet localities. No sure method of obtain- 

 ing them can be given. Unlike the plant and animal cells we 

 have examined, the amoeba has no fixed form. Viewed under the 

 compound microscope, it has the appearance of an irregular mass 

 of granular protoplasm. Its form is constantly changing as it 

 moves about. This is due to the pushing out of tiny projections 

 of the protoplasm of the cell, called pseudopodia (false feet). The 

 outer layer of protoplasm is not so granular as the inner part; 

 this outer layer is called ectoplasm, the inside being called 

 endoplasm. In the central part of the cell is the nucleus. This 



