1919] Boeck: Studies on Giardia Microti 119 



Summary 



From the data which has been reviewed in the foregoing pages the 

 following facts regarding the life cycle of G. microti are established. 



There are two distinct phases in the life history of the flagellate : 

 the one a free vegetative phase; the other encystment. 



During the vegetative phase the animal may pass through the 

 following stages: 



As an adult organism it may undergo mitosis in which case there is : 



Subsequent formation of a two-zooid somatella and later plas- 

 motomy to form two daughter flagellates; or, 



The formation of an eight-zooid somatella, followed by plasmotomy 

 to form eight daughter flagellates; or, 



A single flagellate may encyst. 



During encystment the animal may pass through the following 

 stages : 



By binary fission two daughter flagellates may form within the cyst 

 which will be liberated when the cysts are ingested by another host. 



By multiple fission an eight-zooid somatella may be formed which 

 will be liberated to complete plasmotomy upon the ingestion of the 

 cyst by another host and the digestion of the cyst wall. 



In case cysts should be ingested before they have completed either 

 binary or multiple fission, a somatella would be liberated upon the 

 digestion of the cyst wall which would continue its development as a 

 somatella in a free state. 



