Cleavage of the Sea Urchin Egg Recovered From the Cleavage-Blocking Effect of Demecolcine***

In the preceding paper (1961), the author reported that demecolcine, one of the derivatives of colchicine, blocked the cleavage of sea urchin eggs as colchicine did.Eggs treated with demecolcine a t concentrations between lo-' and 3 x lO-'% for 1 hour could resume cleavage when washed with normal sea water, and developed to gastrulae quite normally both in shape and in size.However, the mode of cleavage in the recovered eggs was found to be markedly abnormal, seemingly correlating with size, number and localization of the mitotic apparatus in the treated eggs.In the present paper, detailed observations on morphological changes manifested in the course of early development of the eggs are described.' $ Contributions from the Seto Marine Biological Laboratory, No. 368.-_ _ _