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Undine

Undine, a species of female water-sprite, possessing a human body, and capable upon marriage with man of receiving a soul. La Motte Fouque, in his exquisite story Undine, gives us an example of such a wayward spirit, who was brought up by a fisherman and his wife, and greatly perplexed them by her vagaries till her marriage with a wandering knight humanized her. Her husband eventually lost her through his unfaithfulness, and she returned to her native element.