The Protozoa 57 



may continue to live and later form additional sporozoites, 

 as in sarcocystis. 



Encystment. Nearly all of the protozoa are capable at 

 times of encysting themselves, i. e., surrounding themselves 

 with dense capsules by which life may be preserved for some 

 time amid such unfavorable surroundings as excessive cold, 

 excessive dry ness, and absence of food. Sometimes the 

 encysted stage is the spore stage (coccidium), sometimes it 

 is the adult stage (ameba). Under these circumstances we 

 find an analogy with the sporulation of the bacteria which is 

 not for purposes of multiplication, but for self-preservation. 

 The encysted protozoa are less hardy, however, than the 

 bacterial and other plant spores, and succumb to compara- 

 tively slight elevations of temperature. 



