THE KIXF/rOSO:\IK IN DEVKLOI^MKXT 91 



An analysis of the comparative niorpli()l()<!;y of ciliates has 

 led to the conclusion tliat th(^ period of pi'iMJivision cor- 

 responds to a phylogenetically primitive structure, whether 

 it is the pattern of kineties which is involved, or the posi- 

 tion of some specialized systems. A non-cellular organism 

 may therefore exhibit primitive and evolved features at 

 different phases of its cycle. But as a matter of fact, 

 changes are seen in the cortex only. Cortical events can 

 not be anything else than the reflection of chemical changes 

 controlled by enzymes and food. Nevertheless, the move- 

 ments of cortical particles, because these particles are or- 

 ganized, can be understood only if the hypothesis of inter- 

 actions between different types of associated particles is ad- 

 mitted. Any change in metabolism may bring about a 

 rupture of an unstable equilibrium, the multiplication of 

 some of the elements creating new poles of attraction, and 

 an origination of new morphogenetic fields. 



Let us quote here another of Paul Weiss's statements 

 (1947): "No model of a cell can be pertinent unless it 

 takes into account both the elementary processes and their 

 organizational frame. Manifest cell organization results 

 from the response of organized elements to fields of or- 

 ganized (i.e., non-random) physical and chemical con- 

 ditions. . . ." 



This statement, like the whole concept of "molecular 

 ecology," may be applied directly to ciliates. Molecular 

 ecology w^as a purely theoretical concept. The study of the 

 dynamic aspects of kinetosomes during ontogeny and phy- 

 logeny of ciliates illustrates the importance of self-reproduc- 

 ing particles in developmental phenomena. 



This study also shows the importance of cortical struc- 

 ture in organization and finally leads to a hypothesis con- 

 cerning the interaction of the different building blocks 

 which may throw some light on the problems of division 

 and differentiation and on the mysterious fact that one 

 single particle can exhibit so many types of activity. 



