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1. Inhibition of activation of Nereis eggs by trinitrophenol, with concurrent sensitization of the eggs to subsequent stimulation, appears to depend on the nitrogroup in the para-position on the phenol.2. The rate of the sensitization process is enhanced by anoxia, CO2, inhibitors of the cytochrome system, or increased potassium ion concentration, but is insensitive to several other inhibitors, narcotics, stimulating agents, and to calcium ion deprivation.3. The immediate initiation of activation by various chemical procedures requires the presence of the calcium ion, is assisted by the potassium ion, `and slightly depressed by increasing magnesium ion concentration, but is not affected by anoxia or by various metabolic poisons.4. Subsequent nuclear and cytoplasmic reorganization, ensuing some minutes after the initial disturbance, is reversibly inhibited by anoxia, inhibitors of the cytochrome system, or diethyl ether.5. Urethane and iodoacetate activate the eggs; this activation is inhibited by trinitro...

1. Germinal vesicle breakdown in Nereis limbata eggs, brought about by heat, or addition of KCl or sodium citrate to the sea water, was inhibited by the addition of picric acid at about M/1000.2. After immersion for a few hours in M/1000 picric acid in sea water, germinal vesicle breakdown occurred upon application of subliminal doses of heat, KCl, or sodium citrate.3. After immersion for 6-70 hours, removal of the eggs from picric acid to ordinary sea water caused germinal vesicle breakdown.4. Activation by ultra-violet irradiation did not conform in these relations to picric acid, under the conditions of the experiments.5. These results are interpreted on the basis of a hypothetical activating substance produced within the egg, and inactivated or bound by picric acid.6. The relation of picric acid to the calcium ion and the combination of calcium with protoplasmic proteins is considered, in an alternative explanation of the results.