ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 77 



The Indian variety being very liable to this disorder is specially 

 suitable for studying the evolution forms of Cercomonas. Numerous 

 observations sbowed that the flagellated Cercomonas changes to a body 

 which repeats the form of the parasitic protozoon. The protoplasm is 

 transparent, but shows a peripheral darkening indicating the presence of 

 a protecting membrane. In this stage, which may be called the 

 encysted or resting stage, no flagella are observable, and it would 

 appear that these are lost during encapsulation. Although all involu- 

 tion forms do not present well marked investing membranes, their 

 protoplasm is always transparent, and the transformation of the 

 protozoon is easily observable. 



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