This study traces the morphological appearance and organization of the cytoskeletal machinery for cell division during the first cell cycle of the sea urchin Hemicentrotus pulcherrimus by immunolocalization of tubulin and DNA. Fertilized and artificially activated eggs are compared in terms of their asters, spindle apparatus and arrangement of chromosomes. Anti-tubulin immunofluorescence microscopy is used to demonstrate the organization of these previous structures at approximately 10-15 min intervals from 40 min-postfertilization through first cleavage. The results revealed that the pattern of microtubule organization and the chromosome cycle were identical to great extent in both fertilized and parthenogenetically activated eggs. However, slight differences, which may not be significant in cell division, were
observed. These differences include the degree of extension and number of astral microtubules, the intensity of staining, and the behaviour and form of chromosome at some stages. The formation of aster microtubule and spindle mitotic apparatus in parthenogenetically activated eggs, in the absence of sperm and its centriole, was
discussed.