Mitosis. Immunofluorescence micrograph of the spindle" in a newly fertilized sea urchin embryo just before cell division. This cell, whose circu- lar outline can just be seen, is in the metaphase of mitosis (division of the nucleus). The spindle is the bright band in the middle, and consists of fibres called microtubules. The dark band in the middle of the spindle is where the chromosomes have lined up prior to being pulled apart into two identical sets. The bright bodies at lower left & upper right are the poles of the spindle, or cen- trioles. The rays of microtubules (asters) around these join the centrioles to the other parts of the cell. Magnification unknown."