THE KTXET(^SOME TX DEVEEOPMENT 93 



logical problems. This will come in a few centuries. For 

 the time being, the biologist has to face such concepts as 

 orienting forces or mor]:)hogenetic fields. Owing to the 

 scarcity of chemical data and to the complexity of life, and 

 despite the progresses of biochemistry, the biologist is still 

 threatened with vertigo. That is why such clear models as 

 the formation of the skeletal pieces of a trichodine are very 

 comforting and useful. 



Unfortunately, most of the constituent parts of the cell 

 are of suj3microscopical size. Therefore special attention 

 has to be given to the rare visible particles, especially to 

 those visible particles endowed with genetic continuity. 

 Such is the kinetosome. 



Considering the history of protozoology, it may at first 

 sight seem strange that so many nature lovers of the old 

 times have been enchanted by ciliates. Of course, watching 

 a ciliate stopping in his search for food to look at you 

 through the microscope is most stirring. But my impres- 

 sion is that the lover of ciliates always had a presentiment 

 that ciliates were to be the proving ground for visible self- 

 reproducing particles. This is how and why we have con- 

 sidered ciliates. 



