LIFE HISTORY OF TWO RARE CILIATES 361 



in the morning. At noon one-half of the number had encysted. 

 The control, supplied with a few Colpidium remained in good 

 condition, no cysts being found. 



The cause of the encystment of the individuals in A may 

 be traced to a too small quantity of Colpidium plus an excess 

 of hay-infusion, previous experience having shown that Spathi- 

 dium will not flourish in a large amount of fluid. Encystment 

 in B was due to an excess of the products of Colpidium metabo- 

 lism the same result having been observed in smaller cultures 

 of Spathidium under similar conditions. Unfavorable tempera- 

 ture conditions probably caused the encystment in C and D. 



By the addition of fresh medium it is often possible to recover 

 Spathidium from the cysts. At 8 o'clock one morning, hay- 

 infusion and Colpidium stock were added to the medium con- 

 taining encysted forms. The cysts were semi-transparent, the 

 vacuole being distinctly visible. At 9.30 the contents of the 

 cysts began to rotate. After half-an-hour, the form of the 

 body was distinguishable. As the rotation continued, the wall 

 of the cyst became more and more transparent and at 12.45, 

 a portion of the protoplasmic contents was extruded beyond 

 the cyst wall. Five minutes elapsed from the time the first 

 portion of the cell-body appeared to the extrusion of the entire 

 protoplasmic mass. 



Upon first emerging from the cyst, Spathidium is weak and 

 shrunken in appearance. The individual under observation 

 remained quiet in the neighborhood of the cyst for several min- 

 utes; then swimming slowly about it paralyzed and swallowed 

 a Colpidium within ten minutes of its emergence from the cyst. 

 Figures 35, 36, 37 and 38 give a few of the stages described, the 

 individual being under constant observation from 8 a.m. until 



1 P.M. 



6. Observations on the life-history 



From a culture of Spathidium started on Februarv 24, 1911, 

 three lines, daughter-cells of one individual, were isolated. The 

 average number of divisions daily of the three lines during the 

 first ten-day period was 1.6. This. was followed by a slight 

 increase in division rate (1.7) during the second ten-day period. 



