OF THE CELL THEORY 177 



and that they appear to be centres from which the 

 spindle threads diverge : the spindle threads them- 

 selves he describes as " apparently muscular," and 

 as governing the movements of the chromatin 

 threads. Van Beneden would therefore regard the 

 pole-bodies as the most important structures, and 

 as really determining cell division rather than the 

 nuclei. Other observers however are not yet 

 prepared to accept this view, but regard the nuclei 

 as the determining agents in all cases of cell divi- 

 sion. 



A still more important problem is as to whether 

 the direct and indirect processes of nuclear division 

 are entirely independent, or whether they are not 

 really related to each other, and if so in what 

 manner. On this point very keen discussion has 

 been and is still being carried on. As regards 

 the relative frequency of the two processes, direct 

 nuclear division has only been seen in comparatively 

 few cases : in leucocytes by Rabl and Flemming ; 

 in the intestinal epithelium of Crustacea by 

 Frenzel ; in regenerating tissues by Fraisse ; in 

 the Infusorian Euplotes by Mobius ; in the early 

 stage of spermatozoon formation in Amphibia, and 

 in a few other cases. On the other hand indirect 

 nuclear division, or mitosis, has been seen in both 

 animal and vegetable cells of almost every kind, 

 and in processes both normal and pathological, and 

 would certainly appear to be by far the more usual 

 method. 



With reference to a possible relation between 

 the two methods, Waldeyer has strenuously main- 



M 



