Comparatively few papers on the galvanotropic reactions of coelenterates have been published and so far as I know there are only two bearing directly on the questions here considered. T h e first is by Pearl', who finds that.when any, except the very strongest, galvanic currents are passed transversely through hydra the animal contracts most strongly on the anode side so that the free end-which may be either oral or aboral-swings around and points towards the anode. T h e tentacles, however, behave differently. W i t h weak currents only those tentacles which are parallel to the current lines contract, but of these the one towards the cathode has a tendency to contract most strongly. When the whole animal has become oriented the tentacles curve slightly so as to become concave on the side towards the cathode. T h e second observation is by Greeley and will be considered in detail later on.
T h e tentacles and manubrium of Polyorchis penicillata, which occurs abundantly in San Francisco Bay during certain seasons of the year, furnish excellent material for the demonstration of galvanotropic reactions, responding to the current in some respects like the tentacles of hydra, but with greater distinctness. T h e method of experimentation consisted in cutting the medusz _ ~_ _