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PHYSIOLOGY 



that they make new organisms like themselves. This 

 power is called reproduction. It belongs to all organ- 

 isms alike. In one-celled animals the process is of 

 course very simple, but it does not differ very widely 

 in its essentials from the process as it exists in higher 

 animals. 



In One-Celled Animals. — The simplest form of the 

 process is called fission. A one-celled organism splits 



mtc 



Fig. 52.— Paramecium. A, Fissicn; 2?, Conjugation. (From Sedgwick and Wilson, 

 after Calkins.) m, mouth ; mac, mic, nucleus. 



into two and in place of the single individual there are 

 two half-sized individuals. These grow and the process 

 is repeated. After a time the animals seem to lose their 

 vigor and are unable to divide unless the protoplasm is 

 rejuvenated. This is accomplished through a process 

 called conjugation. Two animals apparently alike come 



