118 Regulation of Size in Unicellular Organisms 



paring the sizes, the mean size at 14 days after en- 

 domixis is taken as 100 per cent, because the body 

 length happened to be greatest in all lines on this day. 

 Erdmann believed that these data demonstrated the 

 existence of a regular progression of sizes, increasing 

 from endomixis up to 14 days, and then declining. 



12 14 16 16 20 22 



Days after endomixis 



Figure 34. Fluctuations in body length, and in body volume (calculated 

 as / X b 2 ), in a clone of Paramecium aurelia at various phases of the cycle 

 of endomixes. Each point is the mean from the measurement of 120 in- 

 dividuals. Temperatures 24° to 26°C. (Data of Erdmann, '20, p. 99). 



But the small amounts of change which were actually 

 found do not indicate that the differences were signifi- 

 cant. They become of a surety not significant when 

 body volumes are calculated by taking into account 

 the breadths as well as the lengths of the individuals 

 (figure 34). If the differences were even larger they 

 might still be due to inequalities of cultural conditions 

 from day to day. 



Size at endomixis. What it would be most desirable 

 to know is whether there are size differences upon the 

 day or two immediately at endomixis and just after it. 



