288 THEORETICAL BIOLOGY 



In considering the whole process, we can distinguish two 

 acts — the division and the duphcation. The protoplasm of 

 the cell is simply divided into two halves, which form two 

 new spheres. Since the protoplasmic mesh-work ever3rwhere 

 consists of like elements, and the amount of protoplasm plays 

 a secondary part, division suffices here, without an actual 

 duplication coming in. But with the chromatin it is different. 

 The chromatin is the bearer of the genes, and in order to 

 distribute these equally to the two daughter-cells, they must 

 first arrange themselves in rows, and then the opportunity is 

 given for them to become paired by duplication. Then at 

 division there go to each half the same number of all the kinds 

 of genes present in the original celJ. At the same time the 

 rearrangement of the chromatin into chromosomes gives a 

 chance in certain cases for the division to result in nuclei 

 with unlike chromatin constitution. 



In normal division, however, where the material bearing 

 the heritable properties is equally distributed, there is an 

 actual duplication corresponding to that of the centrosomes. 

 Even in the case of the centrosomes, we cannot speak of a 

 simple division, because each of the two that arise corre- 

 sponds in every particular to the original one. 



The whole process is complicated by the fact that, in 

 addition to the division of the protoplasm and the duphcation 

 of the centrosomes and chromosomes, two other processes come 

 in successively, processes involving movement and shaping. 

 The one effects the transformation of the spongy chromatin 

 into four discrete chromosomes ; the other relates to the 

 development of the division-spindle, the protoplasmic threads 

 of which serve to separate the duplicated chromosomes from 

 one another and draw them to their centrosomes. Lastly, 

 the degeneration and the re-forming of the nuclear membrane 

 comes into the process in complete conformity with plan. 



These are all independent processes, which are connected 



