Mitosis is arbitrarily divided into five linearly ordered stages. In each of these stages events occur which lead to the ultimate goal of cell division. This division must be carefully executed in order to ensure that a cell does not have too many or too few chromosomes. It is for this end that centrosomes are used. In the early stages of prophase, centrosomes duplicate themselves in order to make sure that when the cell divides itself there will be two poles and enough centrosomes for the daughter cells to use. While this is happening chromatin is winding up into chromosomes, so it can be easily and equally sorted between the two daughter cells. The nucleus must now be destroyed by various enzymes in order to ensure that it does not get in the way of the movement of the chromosomes. During this time, the nucleolus disappears only to reappear later in the last stage of mitosis. During the later stages of prophase, chromosomes are moving away from each other in accordance with the law of diffusion. The centrosomes start to move to opposite sides of the cell. The centrosomes also begin to organize the mitotic spindle, which are composed of microtubules. These formations are dubbed asters that are believed to assist in the maintaining of the structural integrity of the cell during the later stages of mitosis. The next phase of mitosis is that of prometaphase or late prophase, as some call it. In this phase kinetochores, small protein complexes, attach themselves to either side of the sister chromosomes’ centromere. The kinetochores are, in turn, attached to kinetochore spindle fibers whose poles are now located on opposite sides of the cell. The kinetochore spindle fibers pull on the chromosomes from each direction with more or less the same strength. The polar spindle fibers now overlap to ensure a stable cellular division. Although the chromosomes are attached to the spindle fibers, there is no alignment of the chromosomes. The next step of mitosis is metaphase; metaphase starts when the chromosomes are aligned and form the metaphase plate. This denotes the location of the future axis where the two cells will be evenly split. Metaphase is called metaphase because it is the phase between the preparation and the execution of cell division. Anaphase is the beginning of the execution of cell division. During anaphase, sister chromosomes are pulled away from each other by opposing kinetochore spindle fibers. This ensures that each daughter cell has and equal amount of chromosomes. While this is happening, the cell membranes are pulling away from each other and starting to begin the furrowing process. During telophase, the nuclear envelope is reformed and the cleavage is clearly visible. Chromosomes now unravel to become indistinct chromatin and the nucleoli reappears. The process of mitosis is over, now cytokinesis, the splitting of the cytoplasm, will complete the division into two, genetically identical, daughter cells.