Periodicity of Cytoplasmic Cycle in Nonnucleate Fragments of Sea Urchin and Starfish Eggs*: (cortical tension/sea urchin/starfish/cytoplasmic cycle).

Fertilized eggs of the sea urchin, Hemicentrotus pulcherrimus and the starfish, Asterina pectinifera were separated by manual bisection to obtain pairs of nucleate and non-nucleate fragments. Simultaneous observation on the pair revealed that the cyclic change in the cortical tension in the non-nucleate fragment was definitely prolonged than the cleavage interval of nucleate partner by about 30%. Activated non-nucleate cytoplasmic fragments derived from the unfertilized eggs and colchicine treated whole eggs of H. pulcherrimus still showed the same degree of prolongation.