ACTIVATION OF CUMINGIA AND ARBACIA EGGS BY BIVALENT CATIONS

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Abstract
1. When unfertilized Cumingia eggs are placed in 0.3 M CaCl2, 100 per cent of the eggs of some individuals undergo apparently normal cleavage. The time of polar body formation and of the first cleavage in eggs activated by Ca is approximately the same as the time of polar body formation and of cleavage in eggs activated by sperm. 2. Polar body formation and cleavage in Cumingia eggs proceed normally in 0.3 M CaCl2 at the various pHs between pH 6.2 and pH 8.6 but are inhibited above and below this range. 3. The bivalent cations Sr, Ca and Ba are able to activate Cumingia eggs and are named in the order of their effectiveness. 4. The time of polar body formation in Cumingia eggs activated by isotonic solutions of SrCl2 and BaCl2 is approximately the same as the time of polar body formation in eggs activated by sperm. 5. The monovalent cations K and Na and sea water inhibit activation of Cumingia eggs by Ca. The percentage of activation decreases as the K/Ca, Na/Ca and sw/Ca ratios increase. K has a greater inhibiting effect than Na. 6. Ba inhibits the activation of Cumingia eggs by Ca, Sr inhibits very slightly the activating effect of Ca, while Mg does not appear to have an inhibiting effect on activation of eggs by Ca. 7. When unfertilized Arbacia eggs are placed in 0.3 M CaCl2, from 40 to 60 per cent of the eggs of most individuals undergo cleavage if the pH of the solution is between 8.8 and 9.2. No membrane is elevated in isotonic salt solutions. 8. Below pH 8.8 the percentage of cleavage is low and above pH 9.0 the percentage of cytolysis is high in Arbacia eggs activated by isotonic CaCl2. 9. Isotonic solutions of SrCl2, BaCl2 and MgCl2 are able to activate a certain percentage of Arbacia eggs, but these ions are not so effective as Ca and their action is somewhat variable. 10. The monovalent cations Na, Li and K in certain definite proportions increase the percentage of cleavage induced by Ca while in other proportions they have the opposite effect. Similarly isotonic NaCl, in certain definite proportions increases markedly the percentage of activation by the Mg solution while in other proportions Na has the opposite effect. 11. Sr, Mg and Ba inhibit the activation of Arbacia eggs by Ca, the inhibiting effect increasing as the Sr/Ca, Mg/Ca and Ba/Ca ratios increase. 12. The results are brought into relation to the colloid chemical theory of stimulation.