134 RESEARCH IN PROTOZOOLOGY 



split while new flagella grow out to complete the normal number. 

 Multiple fission was also described for both the active state and for 

 cysts of G. muris by Kofoid and Christiansen, for the cyst of G. 

 microti by Boeck, and the cyst of G. enterica by Kofoid and Swezy. 

 In multinucleate cysts there were often two sizes of nuclei, suggest- 

 insr maturation but no reduction of chromosome number was ob- 

 served. The interpretation of these multinucleate cysts (up to six- 

 teen nuclei) with only two or four axostyles remains obscure, 

 especially since never more than two animals have been seen in a 

 cyst. 



2. Encystment 



Encystment in trichomonad flagellates is a subject about which 

 there is much difference of opinion although cysts regularly occur 

 for Chilomastix, Hexamitus and Giardia. Tritrichomonas muris 

 tends to round up soon after the death of the host unless kept at 

 the body temperature of the host. The rounding-up process passes 

 through a stage during which the anterior flagella and the undulat- 

 ing membrane remain active, causing the animals to rotate. Even- 

 tually, however, a stage is reached, the surface of which is smooth, 

 and the organelles become entirely withdrawn within the cytoplasm. 

 In fixed and stained preparations these completely rounded stages 

 stain more intensely than trophozoites, indicating the more con- 

 densed condition of the protoplasm that characterizes many cysts. 

 Furthermore the contained organelles appear to be entirely normal, 

 degeneration therefore not being indicated. Occasionally similar 

 fully developed spherical stages are found on slides prepared im- 

 mediately after the death of the host, when the great majority of 

 the individuals retained their normal vegetative shape, suggesting 

 that such stages are a part of the life cycle and not always mere 

 reactions to a changed environment. The writer has therefore been 

 led to believe that these completely rounded stages are the biologi- 

 cal equivalents of cysts although he has thus far been unable to 

 demonstrate a true cyst membrane. A number of other investiga- 

 tors have interpreted these completely rounded up stages of T. 

 muris as cysts, for example, Wenyon (1907), Kuczynski (1914) 

 and Mayer (1920). 



The Chilomastix of the rat forms a cyst (Fig. 13, b) that very 

 closely resembles the cyst of C mcsnili of man. Division within 

 these cysts has not been observed, but has been described for the 



