80 



CELL-DIVISION 



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

 ter-granules (Spalthalften) to the daughter-cells."! "In my opmion 

 the^'chromosomes are not independent individuals, but only groups of 

 numberless minute chromatin-granules, which alone have the value 



of individuals."^ 



These observations certainly lend strong support to the view that 

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

 a cono-eries 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 

 archoplasm, or in the last analysis, the centrosome. 



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 o-ive 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-" 

 sion of its total mass, but not of its individual elements or chromatin- 

 granules (Fig. 40). 



Before the discovery of mitosis, nuclear division was generally 

 assumed to take place in accordance with Remak's scheme (p. 45)- 

 The rapid extension of our knowledge of mitotic division between 

 the years 1875 and 1885 showed, however, that such a mode of 

 division was, to say the least, of rare occurrence, and led to doubts 

 as to whether it ever actually took place as a normal process. As 

 soon, however, as attention was especially directed to the subject, 



1 '93, pp- 203, 204. " ''■'^•' P- -°5- 



