CHAPTER 11 



Differeiiliation in Ciliates 



Development of an organism, as already stated, may be 

 considered from the angle of cell diversification. Is it pos- 

 sible to trace homologous phenomena among ciliates? To 

 what extent are differences of the various sectors of a ciliate 

 equivalent to cell differentiation? 



In apostomatous ciliates, these differences are, at least 

 partially, responsible for the specific structure of the ciliary 

 system. But, by definition, differentiation is not reversible. 

 And there often exists in cells of higher organisms a marked 

 antagonism between differentiation and division. Many 

 differentiated cells are unable to divide. Since ciliates di- 

 vide, one could be tempted to conclude that ontogenesis of 

 ciliates has in common with ontogenesis of Metazoa only its 

 quality of ontogenesis. Let us compare the morphogeneti- 

 cal processes in some ciliates. 



In ciliates of the Leucophrys type, the proter and the 

 opisthe are modelled in the anterior and posterior parts of 

 the parent. The infra-equatorial part, between the kinety 1 

 (stomatogenic) and the last kinety n, becomes the oral zone 

 of the opisthe. In this case, apparently, no element of the 

 cortex has undergone irreversible change. 



In the hypotrichous ciliate Euplotes, the argyrophylic 

 cortical network is entirely reorganized at each division, 

 starting from non-visible building blocks. 



The oral ciliature of the opisthe will be formed by divi- 

 sion and organization of an anarchic field of kinetosomes. 

 The old parental structures disappear; cortical network and 

 cirri are reorganized : the parental mouth is reorganized into 



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