THK CAUSE AND NATURE OF ENCYSTMENT. 



It was not only found that when Polytomella is so transferred 

 from culture to culture for some time their tendency to encyst 

 becomes practically negligible, but also that marked morpho- 

 logical changes occur. When encystment is thus prevented for 

 some time the organism will frequently show considerable de- 

 crease in size, almost invariably the cytoplasm will become 

 coarsely vacuolated, and the starch entirely disappear. Fig. ic 

 was taken from series 4 on the fourteenth day after seeding; 

 Fig. id from series Ai on the sixtieth day. In series Di, D2, 

 DT,, Ei, E2, and 3, it was noticed that all contained little starch. 

 In living mounts the cell-body was quite clear and the size above 

 normal. Fig. le was taken from 2 on the eighteenth day. The 

 abnormally large size was lost as soon as the numbers began to 

 decline. Eventually all of these cultures showed only a few 

 degenerate, vacuolated individuals. 



It was thought desirable to determine whether or not these 

 degenerate forms could give rise to healthy cultures. Accord- 

 ingly, series F was started. The history of these cultures has 

 already been given, with the exception of the data found in 

 Fig. 2. Fig. 20, was made from a typical individual taken from 



FIG. 2. Camera-lucida outlines showing variations in size. Figure e vacuo- 

 lated. (See text for explanation.) Magnification 1825 X. 



