20 



Regulation of Size in Unicellular Organisms 



datum, using the same methods as in the above work. 

 He did not put together the results at various ages, 

 because he studied primarily the modifications in rate 

 of growth produced by certain chemical substances; 

 but it seems a legitimate procedure to average his data 



6 1£ 18 24 



Time after beginning constriction in hours 



Figure 6. Growth in length and in volume during the life of an individual 

 Paramecium caudatum. For each point plotted, 24 to 188 individuals, derived 

 from one clone, were killed and measured in length and in breadth. The 

 relative volumes were calculated as average breadth squared, multiplied by 

 average length, or / X b 2 . (Data of Jennings, '08). 



for all Paramecia grown under control or standard 

 conditions during his experiments. When this is done, 

 the curves shown in figure 7 for length and for volume 

 are obtained. Again the gain in length is rapid at first 

 and later almost nil. But the gain in volume is exceed- 



