174 Regulation of Size in Unicellular Organisms 



wig ('02) saw in this a relationship which was possibly 

 a general one. He ('03) gave to it a theoretical im- 

 portance, for he suggested that the size of the nucleus 

 controlled the size of the body. A certain bulk of 

 nucleus presided over the accumulation of so much 

 cytoplasm; when this much had been attained the nu- 



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Time after fission in hours 



Figure 57. Growth in volume of the nucleus and in the ratio of body volume 

 to nuclear volume during one generation in Paramecium caudatum at 25 °C. 

 Volumes were calculated as / X b X t. Each point represents one individual 

 fixed and measured. The body volumes of the same individuals are shown 

 in figure 8. (Data of Popoff, '09). 



cleus was forced suddenly to double itself, and fission 

 of the body occurred. This was, therefore, a possible 

 mechanism of fission which included in it a means of 

 regulating body size; though ultimately it left open 

 the question as to what controlled the rate of assimila- 

 tion on the part of the cytoplasm, a physiological ques- 



