90 THE BIOLOGY OF ST EN TOR 



detorsion of the lateral striping (kinetics) preceding fission, and 

 thus apparently return to a more primitive state of differentiation, 

 Lwoff (1950) maintained that division does require a more 

 embryonic state and that '* The ciliates have solved the problem of 

 perpetuating complex adult structure by cyclical dedifferen- 

 tiation ". Although this statement may apply to apostomes and to 

 forms like Euplotes which form new^ feeding organelles for both 

 proter and opisthe, it is not apropos of Stentor in which pre- 

 existing cytoplasmic differentiations are obviously passed on to 

 the daughter cells, and therefore cannot be generalized. I think 

 that the important point is that most ciliates do not dedifferentiate 

 before or during fission until they are quite formless and then 

 divide. For it is apparent enough in the example of Stentor that 

 maintenance of the complex structures of lateral striping which 

 continue their ciliary and contractile functions throughout this 

 process and are simply cut in two is not incompatible with 

 division, and that therefore cell division does not necessarily require 

 that a cell regress below a high state of differentiation. 



Persistence of cortical differentiations in dividing stentors also 

 precludes surface tension changes as a means of cell division in 

 these forms and their allies, and the separation of asters in a 

 mitotic figure is also ruled out. Studies on cleaving eggs in which 

 these and other forces seem to be operating hence cannot be taken 

 as characteristic of all cell divisions. Perhaps we can learn from 

 Stentor of other factors equally important or effective, especially 

 with regard to multiplication of tissue cells. It has been amply 

 demonstrated above that stentors can be operated upon during 

 fission in many ways which afford a promising approach to prob- 

 lems of cell division, as it has also been shown that the questions 

 of differential growth even within the confines of a single cell are 

 in this organism amenable to experimental analysis. 



