THE CELL AND CELL DIVISION 63 



somes ; and that certain achromatic elements became specialized into a 

 spindle, also at first intranuclear (linin), and at present in nearly all 

 forms both intra- and extranuclear in origin. The chromosomes we 

 must now consider more particularly. 



Interest in the process of mitosis centers in the chromosomes 

 and their behavior, for, as we have said, this whole process seems 

 to be directed toward the equal distribution of the daughter 

 chromosomes to the daughter cells, while the cytoplasm may 

 or may not be equally divided at the same time. We do not 

 know how the constituents of the nucleus other than the 

 chromosomes are distributed in cell division. There is little 

 reason for supposing that these are distributed with exact 

 equality. 



We may recognize two chief aspects of chromosomal behavior 

 in mitosis. The first is the division of the chromatin granules 

 or chromioles composing the chromosomes; these granules all 

 divide in the same direction so that the total result appears as 

 an exactly equal longitudinal division of each chromosome, or 

 of the spireme in those cases where the division of the granules 

 occurs very early. This is the essential act of chromosome 

 reproduction and it is obviously a process concerning the 

 chromatin alone, independent of the remainder of the mitotic 

 mechanism. The second important fact is the distribution of 

 the two chromosome halves or daughter chromosomes to the 

 two daughter cells. This is accomplished by the extra-chromo- 

 somal elements of the mitotic figure, the chromosomes apparently 

 taking a purely passive part in the process. We see in the 

 mitotic figure, not a mechanism for cell division merely, for this 

 is frequently accomplished in the absence of mitosis, nor for 

 chromosome division, for this frequently precedes the formation 

 of the mitotic figure; but essentially the mitotic figure is a 

 mechanism effecting the equal distribution to the daughter 

 cells of the products of chromosomal division within the nucleus 

 of the parent cell, so that each new cell has a complete group of 

 chromosomes similar to those of the parent cell. The precision 

 and wide occurrence of this equal distribution, through mitosis, 

 of the chromosomes and of these cell organs alone, leads to 



