10 



Regulation of Size in Unicellular Organisms 



of such vacuoles. It is characteristic of individual pro- 

 tozoa, though not of clones or of species, that in the 

 same medium the final sizes of successive vacuoles are 

 relatively uniform. This is indicated for Ameba in 

 figure 3. 



In table 1 are presented the data obtained by various 

 observers for the rates of water output through vacu- 

 oles in numerous species. Unfortunately most of the 



Table 1. 



Rates of Turn-Over of Water Through the Contractile Vacuoles of Various Ciliates and 



[of Ameba 



data are extremely approximate, for only the frequen- 

 cies of emptying were measured on living individuals, 

 whereas the vacuolar sizes, which may not be maxi- 

 mal or may be super-maximal, were taken upon fixed 

 specimens. But for Ameba (Adolph, '26; Botsford, 

 '26; Howland and Pollack, 27) the same vacuoles 

 which were timed were also measured at the time of 

 bursting. 



Setting aside the question of the essential functions 



