114 



CELL-DIVISIOX 



independent reproductive act of the chromatin. The reconstruction 

 of the nucleus, and in particular the breaking up of the chromosomes 

 after division into small granules and their uniform distribution 

 through the nuclear cavity, is, in the first place, for the purpose of 

 allowing a uniform growth to take place ; and in the second place, 

 after the granules have grown to their normal size, to admit of tJicir 

 precisely equal gnautitative and qualitative division. I hold that all 

 the succeeding phenomena, such as the grouping of the granules 

 in threads, their union to form larger granules, the division of the 

 thread into segments and finally into chromosomes, are of secondary 

 importance ; all these are only for the purpose of bringing about in 

 the simplest and most certain manner the transmission of the daugh- 

 ter-granules (Spalthalften) to the daughter-cells."^ " In my opinion 

 the chromosomes are not independent individuals, but only groups of 

 numberless minute chromatin-granules, which alone have the value 

 of individuals." ^ 



These obser\'ations certainly lend strong support to the view that 

 the chromatin is to be regarded as a morphological aggregate — as 

 a congeries or colony of self-propagating elementary organisms 

 capable of assimilation, growth, and division. They prove, more- 

 over, that mitosis involves two distinct though closely related factors, 

 one of which is the fission of the chromatic nuclear substance, while 

 the other is the distribution of that substance to the daughter-cells. 

 In the first of these it is the chromatin that takes the active part ; 

 in the second it would seem that the main role is played by the 

 amphiastcr. 



E. Direct or Amitotic Division 



I. General Sketch 



We turn now to the rarer and simpler mode of division known 

 as amitosis ; but as Flemming has well said, it is a somewhat trying 

 task to give an account of a subject of which the final outcome is 

 so unsatisfactory as this ; for in spite of extensive investigation, we 

 still have no very definite conclusion in regard either to the mechan- 

 ism of amitosis or its biological meaning. Amitosis, or direct division, 

 differs in two essential respects from mitosis. First, the nucleus 

 remains in the resting state (reticulum), and there is no formation 

 of a spireme or of chromosomes. Second, division occurs without 

 the formation of an amphiaster; hence the centrosome is not con- 

 cerned with the nuclear division, which takes place by a simple 

 constriction. The nuclear substance, accordingly, undergoes a divi- 



1 '93, pp. 203, 204. 2 /.^.^ p. 205. 



