1. The eggs of Thalassema neptuni are stored in the nephridia and, as the result of their compression by the muscular walls of these organs, are distorted in shape. This distorted shape is maintained until maturation begins. Activation, whether normal or artificial, is accompanied by the adoption of a spherical shape by the egg. This change probably indicates an increase in the permeability of the egg membrane to water and forms a useful index of activation.

2. Artificial parthenogenesis of the eggs of Thalassema neptuni can be induced by means of isotonic salt solutions.

3. At the hydrogen ion concentration of sea-water the chlorides of sodium, lithium, and potassium are incapable of causing development of the unfertilised eggs, but calcium chloride is an efficient activating agent.

4. Mixtures of calcium chloride with the chloride of an alkali-metal in certain proportions cause parthenogenesis.

5. For series of potassium-calcium mixtures two maxima for activation are obtained, one where the calcium concentration is high and one where it is low. Sodium and lithium in presence of low concentrations of calcium are much less effective than potassium.

6. For all the activating solutions tested two optimal times of exposure are found at about 6-9 min. and 30 min.

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