230 GARY N. CALKINS 



resting stages of non-conjugating forms, four in organisms pre- 

 paring to encyst, and as many as sixteen in the conjugating ani- 

 mals. Owing to the difficulty in finding them even in the most 

 carefully stained sections, no positive statement can be made as 

 to the 'normal' number, but it appears to be four. They are 

 very minute (4-6 n) with relatively little chromatin, usually 

 concentrated in a few central granules, and with definite nuclear 

 membranes. The division spindles are narrow and sharply 

 pointed with the chromatin in minute chromosomes (fig. 7). 

 ^ In addition to the nuclei there are numerous curious and enig- 

 matical structures in the endoplasm which I am unable to inter- 

 pret. These are often in the form of spindles with curious rod- 

 like bodies which suggest chromosomes (fig. 7). These are 

 found during all stages of vegetative life. There is no evidence 

 of their division and no reason to believe that they are nuclei, 

 and the only suggestion I have to offer as to their function, is 

 their possible connection with the formation of new seizing organs 

 to replace those used up in food capture. 



THE LIFE CYCLE 



In other places I shall describe the details of encystment and 

 of conjugation, and will limit the present paper to the history of 

 the race from October 28th to the present time (April 20) . Thus 

 far the organisms have gone through two completed cycles, 

 each ending in encystment of all the living material and during 

 which nuclear reorganization occurred. 



The initial cycle (October 31 to December 28): Individual X 



Five lines derived from individual X were each changed to 

 fresh water and fed 9 Paramecium caudatum daily. The daily 

 rates of division were averaged for 5-day periods and the results 

 plotted to give the accompanying chart A. The daily records 

 include the number of divisions which each individual had 

 undergone during the preceding twenty-four hours, the number 

 of living Paramecium in each culture dish, the number that 



