THE BUILDING-STONES OF THE ORGANIC WORLD 83 



At first the two chromosome-halves are still connected with 

 each other by fine colourless filaments or fibres, but soon a 

 dividing wall arises from the margin of the cell towards the 

 centre, and with it the last connection between them disappears 

 (fig. 23, 5 ). The division is now essentially complete; it only 

 remains for the chromosomes in the young daughter-cells to 

 change into new resting nuclei. This is done in the last act of 

 indirect nucleus-division, the telephase. As soon as the chromo- 

 somes have arrived in the neighbourhood of the central bodies 

 they all range themselves in close formation. They form pro- 

 jections and in the interior we observe the appearance of vesicles 

 which become greatly enlarged by the absorption of fluid from 

 the cell and drive apart the chromatin particles. Thus the 

 original chromatin frame is once more restored. Finally a 

 new nucleus membrane is formed, and with that act the nucleus 

 reaches once more a stage of rest (fig. 23, e) . 



There is now no trace of individual chromosomes to be 

 seen : they have been completely dissolved into their chromatic 

 constituents. But this is only apparently so, for as in each new 

 division the chromosomes appear once more in the same form 

 and number, we may assume that, though invisible, they retain 

 their individuality in the nucleus at rest. Several facts confirm 

 this hypothesis. If it accidentally happens during a division 

 that a supernumerary chromosome enters iuto one nuclear half, 

 it will reappear afterwards in all descendants of this particular 

 nucleus. 



On reviewing this wonderful process of mitosis one fact seems 

 to be incontrovertible, namely, that all these complex processes 

 have for their final object the most accurate distribution of the 

 chromatin, the hereditary substance, among the nuclei of the 

 daughter-cells. But the nature of the forces here at work, 

 tending with such wonderful precision towards one definite aim, is 

 a deep mystery. It is true that we are able to observe accurately 

 with a microscope every morphological change that takes place 

 during the nucleus-division ; we gain the immediate impression 

 that the central bodies exercise a controlling influence upon all 

 processes and are the real ' kinetic centre ' from which the 

 various motions result, but from a real understanding of this 

 strange play of the forces we are as yet far distant. We are 

 here confronted with one of the deepest riddles of the Universe, 



