82 MORPHOGENESIS IN CILIATES 



of fields which will then fuse harmoniously into the charac- 

 teristic pattern of the parent. 



Of course, when one tries to find what is really specific of 

 division, the only possible answer is: the duplication of the 

 differentiated structures, or the partial or total substitution 

 and superposition of two differentiated structures for the 

 unique parental structure; in other terms, the transition 

 between an organism with one morphogenetic field into an 

 organism with two morphogenetic fields. 



In a dividing cell, with two asters surrounding kineto- 

 somes, the daughter kinetosomes act as if repulsing each 

 other. This model seems far too simple when we are deal- 

 ing with the duplication of morphogenetic '^fields." Never- 

 theless, the equilibrium of two interacting systems, one of 

 them being the kinetosomal system, seems to play an im- 

 portant role in morphogenesis and division of ciliates. This 

 hypothetical concept should of course be submitted to ex- 

 perimental control. 



^But I want to emphasize that this conception of inter- 

 action of two — or more — systems is able to provide an ex- 

 planation of the cyclic formation of trichocysts. Let us 

 suppose that the maximal affinity of the kinetosome is for 

 the building blocks of the orienting system and for the 

 building blocks of cilia. Let us suppose that more kineto- 

 somes are formed than available units of these building 

 blocks, or that the relative speed of their synthesis is low. 

 This would result in "free" kinetosomes which would be 

 able to bind material for which the affinity is low, for ex- 

 ample, building blocks of trichocysts, the result being the 

 formation of trichocysts. 



