76 MORPHOGENESIS IN CILIATES 



resents essentially the sum of the movements of the kineto- 

 somes. Two new '^daughter-patterns" are formed anew at 

 each generation from one or many kinetosomes. The adult 

 ciliate is homologous to an adult organism. The "predivid- 

 ing" ciliate is, to a certain extent, homologous to an egg. 

 Let us remember that most of the apostomes can divide 

 only in the encysted stage, that is to say, after production, 

 like an egg of one, or even two, cystic membranes. Let us 

 remember also that the hypertomite of Phoretophrya and 

 the hypertrophont of Synophrya divide only some hours 

 before the ecdysis of the host. Their division is controlled 

 by an external stimulus and thereby recalls the activation 

 of the egg. 



We have to remember that before each division the oral 

 kinetics of Proboveria and Boveria migrate towards the 

 anterior pole and take up a phylogenetically primitive posi- 

 tion. The situation is here very favorable because the 

 phylogenetic change we have considered is not a morpho- 

 logical "differentiation" but only a change in the position of 

 a system. The conditions, whatever they may be, which are 

 responsible for the movements and equilibrium of the oral 

 structures on the cortex are the result of the changes which 

 take place after division. Some phylogenetically primitive 

 condition reappears before each division. The study of 

 apostomatous ciliates in which a bipolar meridian pattern is 

 produced before division has already allowed the same con- 

 clusion. The differentiated cortex of highly evolved ciliates 

 may thus be compared to the differentiated cells of a meta- 

 zoan. The ''neutral" cytoplasm and the self-reproducing 

 units such as kinetosomes may be compared to the germinal 

 line, in the sense that they are responsible for the "creation" 

 of new organisms. 



Thus, if we consider highly evolved ciliates, we see that 

 the "adult" is unable to undergo division. There is really 

 an antagonism between differentiation, in the sense of com- 

 plex productions of the adult, and division. 



