During oogenesis, both the growth and the differentiation of starfish oocytes are arrested at first meiotic propphase (reviewed in ...). To become capable of fertilization, oocytes of all animals must overcome the arrest and activate meiotic maturation. The availability of large numbers of synchronized oocytes makes the starfish an excellent experimental model system for studying meiotic maturation. Previous studies have shown that immature starfish oocytes exhibit polarized cell morphology. First,the large nucleus (the germinal vesicle , or GV) is located close to the plasma membrane of the animal hemisphere. The cytoskeletal organization of the animal pole is quite different from that of the other regions in that the F-actin layer is missing in the space between the GV and the plasma membrane. Indeed, it is through this"corridor"that the two polar bodies are extruded during the two reduction divisions which are the visual display of oocyte maturation. Second, the cortical region of the oocyte differs form the inner cytoplasm in that actin filaments are ordered in a cluster just beneath the plasma membrane forming a cortical cytoskeletal iayer. In addition, the cortical region is crowded with numerous membrane-bound vesicles filled with stratified contents (schroeder). Because of the presence of actin-binding proteins that polymerize or depolymerize actin filaments, the cortical actin cytoskeleton is in a dynamic equilibrium.