Rates of Growth of Individuals 27 



tion essential, in order that the fissions among its 

 members will not be in step with one another, but also 

 such cultural conditions are necessary as will not 

 change significantly for several days. At present no 

 data of the kind are available; the nearest approach 

 seems to be a certain Paramecium culture of Jennings 

 ('08b). This is analyzed in figure 12 in terms of rela- 

 tive lengths and volumes, the latter being taken to be 

 proportional to the length multiplied by the square of 

 the breadth. Lengths can hardly be used without 

 correction in the case of Paramecium, since Jennings 

 found (figure 6) that the same length may occur twice 

 in one growth cycle, due to the shortening just before 

 fission. By this method the general shape of the curve 

 for growth in length is confirmed, while for growth 

 in volume we already have several types of curve. 



Summary. What shall be considered the normal 

 progression in which body mass is increased in Para- 

 mecium? With respect to length all the data agree 

 that the increase is very rapid at first, and then is slow 

 (with possibly a decrease just before fission). But 

 with respect to volume we have two diverse pictures 

 from two sets of equally well-founded data. Jen- 

 nings's results show that Paramecium accumulates 

 materials rapidly at first, and then more slowly or not 

 at all; Mizuno's results show that Paramecium loses 

 body substance at first, and then gains it at a uniform 

 rate throughout the rest of its individual existence. 

 So far as is now known, both pictures may be charac- 

 teristic; whether the diversity is due to difference of 

 race or difference of environment cannot yet be decided. 



2. Other Species 



Data showing the rates of volume increase of in- 

 dividuals are available for the ciliate Frontonia, the 

 rhizopod Hartmanella, and various bacteria. 



