CONCLUSIONS 231 



and metamonads do divide, temporarily suppressing and then 

 reproducing their flamboyant individualities. It is conceivable 

 that a single genetic system is incapable of meeting these demands 

 and at the same time providing the delicate set of checks and 

 balances necessary for intercellular cooperation in a metazoan 

 organism. The author finds it impossible to visualize with Hadzi 

 and Hanson (see Hanson, 1958) the subdivision of a ciliate-like 

 organism into cellular compartments as a step in metazoan 

 evolution. Comparison of the protozoan with the total metazoan 

 organism does not help, because no known systems of structures 

 in metazoan tissues seem related, morphologically, to ciliate 

 intracellular fiber systems. But certainly, the ultrastructure of 

 lower metazoan ciliated epithelia and of the morphologically 

 simple acoel turbellaria needs to be investigated. 



The incompatibility of cellular complexity and multicellular 

 differentiation is by no means a fresh idea. The only original 

 notion here is that ultrastructure may give us a clue to the nature 

 of a choice that was open to organisms at a protozoan level in 

 evolution. Phytoflagellates, ameboflagellates, and the simplest 

 protomonads possess all the fundamentals of metazoan (and 

 protozoan and metaphytan) cell structure. Higher zooflagellates 

 and ciliates went on to exploit to the full the potentialities of 

 intracellular fibrillogenesis. Those organisms that ultimately were 

 to spawn the metazoa retained the kinetosome/centriole as a 

 versatile, polarized, morphogenetic center but did not enslave it, 

 and their genetic systems, in the service of immediate morphologic 

 elaboration. 



This discussion has been teleologic, and deliberately so. One 

 can afford to be teleologic only when one knows very little, or a 

 very great deal, about the facts, and we know very little. If these 

 notions are attacked with vigor by future workers who are able 

 to marshal more facts to their purpose, then they will have served 

 their function. 



