Size in Relation to Multiplication Rate 93 



by frequently cutting each individual into two viable 

 ones, than in cultures which reproduce in the normal 

 fashion? Slight evidence bearing upon this question 

 may be adduced from an experiment of Phelps ('26). 

 By cutting, about one quarter of the cytoplasm was 

 removed from an Ameba every second day, and this 

 prevented the Ameba from reproducing for 32 days. 

 The total amount removed was about equal, it was 

 reckoned, to 2.4 adult Amebse. But the control ani- 

 mals meanwhile reproduced 3.5 times, giving 12 nearly 

 adult Amebse. Whether in addition to the factor of 

 initial mass there was also some retardation due to 

 the operation itself, one is not justified in calculating 

 from these approximate data. Evidently Ameba is 

 not a suitable organism with which to find out whether 

 more total protoplasm will form after cutting. An 

 organism, such as Stentor, which will grow and repro- 

 duce in both pieces resulting at each cutting, is needed. 



Effect of fission on growth. The soft-bodied uni- 

 cellular organisms are usually characterized by 

 growth up to a certain size, after which fission into two 

 individuals occurs and growth is renewed. Growth is 

 necessary in most instances before fission occurs. But 

 fission is clearly separated from growth, as previously 

 noted; fission is not a slow and continuous process 

 which goes on while growth is proceeding, but comes 

 on after certain requirements have been fulfilled. Ap- 

 parently growth stops in some species several min- 

 utes or hours before fission visibly sets in. 



Were there less separation between growth and fis- 

 sion than actually exists, it would be hard to conceive 

 how the adult size could vary so little as it has been 

 shown to do; there is no rigidity either morphological 

 or mechanical which visibly decides when adult dimen- 

 sions have been reached. The presence of a definite 

 cycle in the growth of individuals of some species 



