Light micrograph of a whitefish cell about to undergo a mitotic cell division, where two daughter cells with with equal & identical chromosomes are produced by cytoplasmic cleavage of the parent cell. The cell is in early prophase, the early stage of mitosis characterised by the condensation of chromosomes and their appearance as the knot of dense, red/black material in centre of cell. The end of prophase sees the dissolution of the nuclear envelope and the formation of the mitotic spindle, a structure that mediates the subsequent movement and separation of the chromosomes as mitosis progresses. Magnification: x315 at 35mm size. Reference: MICROCOSMOS, figure 6.23a, page 122.