CHAPTER II 

 PRIMARY FUNCTIONS OF THE ORGANISM 



WE have seen that protoplasm, although it may 

 be resolved into a mixture of various complex chem- 

 ical substances with a more or less definite physical 

 structure, does not exist as protoplasm per se, but is 

 always organized in certain definite relations, one 

 part to another and to the environment of the whole. 

 The unit of this organization is the cell. 



The individual organism usually consists of many 

 cells linked together in a complex whole, but the 

 individual may also subsist in a single cell. In the 

 latter case we speak of the individual as a Protozoan 

 (or Protophyte, if a plant), and in the former as a 

 Metazoan (Metaphyte, if a plant). As a rule the 

 one-celled organisms (sometimes spoken of collec- 

 tively as Protista) are simpler both in structure and 

 in function than those of many cells. Such, how- 

 ever, is not always the case. The most complex 

 of the Protozoa is as specialized in organization and 

 functions, if not more so, than the simplest of the 

 Metazoa. It would probably be more accurate to 

 speak of the Protozoa as non-cellular rather than one- 

 celled, since the differences between the two groups 

 are qualitative rather than quantitative, i.e. are not 

 based on the number of cells present. So from 



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