Effects of D

When unfertilized sea urchin eggs are treated with D2 O-sea water, fertilization membranes are raised, cytasters appear in the cytoplasm and cleavages occur. Such observations are in agreement with those reported by Gross and his collaborators. However, D2 O-treated eggs can develop at least to the gastrula stage under appropriate conditions, in contradiction to descriptions by Grosset al. This is the case in eggs of three species of Japanese sea urchins used here. The double treatment with D2 O is more effective in inducing parthenogenetic development than the single treatment and, further, double treatments, such as the combinations of D2 O and hypertonic sea water or butyric acid and D2 O, also, can effectively induce the development. In addition, centrifugally enucleated egg-halves can be activated and developed to a blastulalike stage by the double treatment with D2 O.