Abstract
1. Nematocysts were isolated from acontia by extrusion in 1·0 M sodium citrate. The high concentration was necessary to maintain the liberated nematocysts in an undischarged state. 2. 2. Isolated nematocysts were comparatively insensitive to stimuli which normally evoked their discharge in situ. This was true for solutions of low pH and high potassium ion concentration. 3. 3. Both discharge and extrusion of in situ nematocysts could be reversibly abolished by pretreatment of the acontia with magnesium chloride. 4. 4. None of the salt solutions tested caused appreciable discharge of isolated nematocysts at an osmotic strength equal to that of sea water. Increasing dilutions of these solutions, however, caused a progressive increase in discharge. Divalent cations, such as calcium and magnesium caused a marked inhibition of this effect, and may play a role in a nematocyst stabilization.
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