4 MORPHOGENESIS IN CILIATES 



ditions the 'existential and operational prerequisites' for 

 each molecular species or group. The probability of mem- 

 bers of a given species to persist, hence to be found, in any 

 but the appropriate setting, would be extremely low. 



4. ''If the specific existential and operational prerequi- 

 sites for the various molecular species and groups differ at 

 different sites of the cell, different species will automatically 

 become segregated into their appropriate ecological environ- 

 ments. As a result, even a wholly indiscriminate mixture 

 can become sorted out into a definite space pattern. Cer- 

 tain species will assemble in relatively stable combinations, 

 like biotic groups, while others, mutually incompatible, will 

 separate. '^ 



This is a beautiful concept. But it is a theory. Is it 

 possible to obtain some positive data concerning cytoplas- 

 mic units? 



C. Darlington (1944) nas classified all biological cor- 

 puscles into three categories: (1) the nuclear system; (2) 

 the plastids of the green plants or corpuscular system; and 

 (3) what he has described as the "undefined residues of 

 heredity/' not associated with any visible body; this is the 

 "cytoplasmic" or "molecular" system whose constituents are 

 generally known as "plasmagenes." 



"In order that we should find out something more about 

 these free plasmagenes/' writes Darlington in his classical 

 book, "we must try to form a more precise picture of how 

 they live, move, and multiply. It seems likely that they 

 are protein molecules or aggregates. Evidently, they are 

 such that, like true genes, they can arise only from proteins 

 of the same kind apart from mutations. Unlike true genes, 

 however, their reproduction is not controlled by a mechani- 

 cal equilibrium but will be subject rather to conditions of 

 chemical equilibrium genotypically controlled but specific 

 for each type of gene." 



This is also an entirely hypothetical conception. When 

 we study viruses or enzymes, we enjoy the criteria of in- 



