90 



Regulation of Size in Unicellular Organisms 



many generations. Phelps ('26) likewise prevented 

 Ameba from reproducing for as long as one month 

 through this expedient of cutting. 



From these experiments upon Stentor and Ameba, 

 the conclusion may be drawn that the attainment of 

 a certain size is a prerequisite for reproduction. But, 

 conversely, reproduction is not essential to continued 

 vitality and growth of individuals. This would seem 

 to differ from the dictum of Rubner ('12) for yeast, 

 that "only through such processes as result in fission 

 can they live indefinitely". But since growth of the 

 individual under normal conditions does bring on fis- 

 sion, Rubner's emphasis upon the processes leading up 

 to fission, rather than upon fission itself, was undoubt- 

 edly the correct one. 



Age at fission. In Colpoda the body sizes of a popu- 

 lation of adults were compared with the durations of 

 life which were occupied in the attainment of these 

 sizes (Adolph, '29). The mass correlation, which is 

 shown in figure 31, gave a slightly negative coefficient ; 

 that is, the individuals with shorter lives were on the 

 average somewhat larger than were the longer lived 

 ones. But the coefficient was within the error caused 

 by the normal variabilities for duration of life and for 

 adult body size. 



Table 7. 



Correlation of Adult Body Volume with Age at Fission Among the 

 Four Members of Quadruplet Litters in Colpoda. The Coeffi- 

 cient of Correlation is +0.271. (From Adolph, '29) 



