60 MORPHOGENESIS IN CILIATES 



desmas. Before division, the enrolled ciliature of the tro- 

 phont becomes meridian, which means an important 

 shortening. 



It is possible to describe the morphology of ciliates in 

 terms of kinetosomes and their derivatives. The morpho- 

 genesis of a ciliate is essentially the multiplication, distribu- 

 tion, and organization of populations of kinetosomes and of 

 the organelles which are the result of their activity. Kineto- 

 somal order is controlled, at least partially, by the kineto- 

 desmas. Embryologists have been led to postulate the ex- 

 istence of specific patterns of protein molecules or fibers 

 which would appear during embryonic development and 

 play an important role in morphogenesis. F. 0. Schmitt 

 (1941) has in vain tried to obtain evidence for this type of 

 structure. The study of apostomatous Protozoa shows that 

 such fibers do exist and that they play, at least in ciliates, 

 an effective role in morphogenetic processes. 



As these fibers undergo unequal growth during develop- 

 ment, we have to predicate an asymmetrical distribution of 

 the substances controlling the synthesis of the fibrous mate- 

 rial. But, evidently, the problem of asymmetry has been 

 only pushed back, and we have studied the results of asym- 

 metry rather than its cause. 



Finally, we have to recall once more that kinetodesmas 

 are asymmetrical fibers. The problem of the origin of this 

 asymmetry still awaits its solution, just like the problem of 

 the spiral structure of cellulose fibers or of starch molecules. 



