Conclusion 195 



mentation will be required to ascertain whether sur- 

 face tension, surface precipitation, micellar size, or 

 some other quantity, represents the indispensable or 

 limiting property in a least-sized living unit. 



Why fission? It would be possible to avoid the con- 

 sideration of individuality by merely stating that not 

 only a body but also an environment is necessary for 

 life; therefore the individual consists of much more, 

 unlimitedly more, than the body. But a more useful 

 way of putting the question is, what requires unicellu- 

 lar organisms to be subdivided into many small indi- 

 viduals instead of fewer large ones? 



This sort of question is difficult to investigate, be- 

 cause the regulation of subdivision processes was set 

 up at some remotely ancestral time. In existing or- 

 ganisms many other activities cannot be carried on 

 without it. But so was the whole regulation of body 

 size, or of fission rate, or of rate of oxygen consump- 

 tion set going in remote ages. Without a past there 

 is no organism. It is possible that at some by-gone 

 time environmental selection eradicated individuals of 

 a given species which were smaller than some limit and 

 larger than some other limit. But in the sequence of 

 observable generations of individuals, even extreme 

 variants are apparently well within the lethal limits. 

 The normal variabilities for size are tuned to values 

 which seem to keep out of reach of any selective factors 

 which may possibly have once determined their sur- 

 vival value. No traces remain by which such factors 

 can be detected. 



What sort of mechanism is ruling the sizes of in- 

 dividuals? In each generation the body is first being 

 mensurated, and then being inhibited from further in- 

 crease in bulk. Each individual is one unit which is 

 manifesting the numerous innate qualities of its race. 

 In the unicellular body there is little "internal medi- 



