1919] Boeck: Studies on Giardia Microti 115 



contained somatellas in various stages of multiple fission. The absence 

 of part of the cyst wall is interpreted to be due to digestion and a 

 continuance of the process would result in the liberation of the soma- 

 tella. Somatella comprising as many as four zooids were found by the 

 investigators just mentioned, but in no case were eight-zooid soma- 

 tellas found. The case of the four-zooid somatella appears to have 

 resulted from the multiple fission of a flagellate which had never 

 encysted, instead of representing a possible half of the eight-zooid 

 individual which might have come from a cyst. 



In all the multinucleate cysts the axostyle had split to form two 

 daughter axostyles. This is similar to the activity of the parent axo- 

 style during binary fission, but the other organelles were not duplicated 

 which is unlike the condition in binary fission. It is probable that 

 the formation of the other organelles is deferred until the process of 

 plasmotomy begins, that being the time that they appear in binary 

 fission. 



It is evident from all the data at hand that the processes of binary 

 and multiple fission are very similar if not identical in their early 

 stages. Both methods begin with the encystment of a single individual, 

 and the subsequent stages up to the formation of a two-zooid somatella 

 are alike. The process of binary fission ceases when plasmotomy of the 

 two-zooid somatella results in the production of two daughter flagel- 

 lates; but with the formation of the two-zooid somatella the process 

 of multiple fission still goes on. The nuclei have gone through one 

 division to form four nuclei, the four nuclei go through another 

 division and eight nuclei are formed, and these eight nuclei, when 

 they divide, form sixteen nuclei. There are three successive divisions 

 of the nuclei in multiple fission but only one division in binary 

 fission. The two processes differ in that multiple fission does not 

 appear to occur so often as binary fission since the cycle of encyst- 

 ment during which binary fission takes place is shorter than the cycle 

 of multiple fission, if a cycle of multiple fission exists. It is probable 

 also, as has been stated, that multiple fission is initiated by some 

 environmental disturbances and, therefore, may not be cyclic but 

 sporadic in nature. 



The data for binary and multiple fission within the cysts of 

 Giardia microti were taken from preparations made from the meadow 

 mouse. A further collection of data will now be presented to cor- 

 roborate the evidence for binary and multiple fission within the cyst. 

 These further data were taken from a study of the cysts of a species 



