The sea anemone Anthopleura elegantissima responds with characteristic contraction to a pheromone released by wounded conspecifics. The alarm pheromone was isolated by ion-exchange chromatography and identified by chemical and spectroscopic methods as the quaternary ammonium ion (3-carboxy-2, 3-dihydroxy-N, N, N-trimethyl)-1-propanaminium. Median effective concentration of the crystalline pheromone is 3.5 X 10-minus 10 mole per liter of seawater.

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A gross anatomic exploration of the nail unit was performed. The characteristic gross components of the nail unit and its relationship to the digital anatomy are described and presented in detail. Each segment of the nail unit is illustrated both photographically and with artistic illustration. It is our intention that through a simple gross dissection the nail structural unit may be better understood.