Conclusion 193 



tions or functions which are allowed to vary. When it 

 is found how many independent variables are present, 

 if any, then the interdependences can be described in 

 relation to them. The investigator has not the dis- 

 couraging problem of measuring ten or twenty proc- 

 esses simultaneously, for organisms are not built of 

 discrete activities. Instead, organisms represent high- 

 ly co-ordinated combinations of activities; they secure 

 many "degrees of freedom" through subjection to 

 multifarious conditions. This statement involves no 

 assumption as to whether the co-ordination is or is not 

 of a kind existing only in organisms. 



While it is possible in a few species that size is de- 

 termined by a single factor such as duration of life, in 

 most species that have been studied it has been demon- 

 strated that numerous factors and correlatives are con- 

 cerned in the regulation of body size. Hence the prop- 

 erty of specific size is of the character of an "emer- 

 gent." It is not observably the outcome of any com- 

 bination of influences and endowments; yet it is con- 

 catenated with them. This by no means precludes the 

 possibility that cause and effect can be traced when 

 the implications of each of the influences and endow- 

 ments are fully known. 



Unanswered questions. The data available allow of 

 no description of a mechanism by which each individ- 

 ual "knows" when its size has attained a value proper 

 to the frequency of sizes in the race's population. But 

 in certain specific cases it can be stated that the oxygen 

 concentration at the center of the body, or the capacity 

 to ingest food faster than it is required for mere main- 

 tenance, or the body mass which will barely be moved 

 by the cilia, has in each instance attained a limiting 

 value. Whether the same factor which prevents 

 further growth will at the same time induce fission is 

 not known ; growth possibly may come to a stop at one 



