CHAPTER 14 



The Kinetosome in Development, 

 Morphogenesis, and Evolution 



Ciliates provide a model in which a cytoplasmic unit en- 

 dowed with genetic continuity and playing an important 

 role in morphogenesis is seen at work during developmental 

 processes. An important feature of the kinetosome is its 

 polyvalency. The fact that one specific particle is able to 

 synthesize types of organites as different from a functional 

 point of view as a cilium or a trichocyst is very suggestive. 

 Whatever the chemical parenthood of the two structures 

 may be, the facts show the importance of such particles. 

 Their loss or modification w^ould bring about the disappear- 

 ance of many functions. This explains perhaps the great 

 scarcity of plasmatic inheritance. It is possible that many 

 mutations of plasmatic particles are lethal because each par- 

 ticle controls many reactions. 



The nature of the control of the alternative activities of 

 a cytoplasmic unit like the kinetosome remains an acute 

 problem. Many hypotheses may be considered when one 

 tries to understand the possible mechanism by which a 

 kinetosome is turned into a trichocystosome. 



1. The hypothesis of a random mutation can be excluded 

 because all the kinetosomes of one ciliate produce a tricho- 

 cystosome at the same time. 



2. The hypothesis of an induced mutation is difficult to 

 admit. The kinetosome divides into two particles, one re- 

 maining a kinetosome able to produce other ''normal" kine- 

 tosomes, that is to say, cilia-synthesizers. Is the difference 



