Light micrograph showing mitosis - prophase, in whitefish blastula, the centriole has divided and the daughter centrioles have moved to opposite poles of the cell, a centriole plus the spindle fibers. Magnification 1,100x Mitosis, the usual method of cell division, characterized typically by the resolving of the chromatin of the nucleus into a threadlike form, which condenses into chromosomes, each of which separates longitudinally into two parts, one part of each chromosome being retained in each of two new cells resulting from the original cell. The four main phases of mitosis are prophase, metaphase, anaphase, and telophase. Blastula, an animal embryo at the stage immediately following the division of the fertilized egg cell, consisting of a ball-shaped layer of cells around a fluid-filled cavity known as a blastocoel. A centriole is a small, cylindrical cell organelle, seen near the nucleus in the cytoplasm of most eukaryotic cells, that divides in perpendicular fashion during mitosis, the new pair of centrioles moving ahead of the spindle to opposite poles of the cell as the cell divides: identical in internal structure to a basal body.