But another, and not a secondary, curiosity of this ocean-labyrinth is, that it is the habitat of a multitude of marine creatures, not to be seen at home in many other places. Except twice a month, at the neaptides, the lower chambers are filled with the sea; and here live and flourish thousands, upon thousands of those mollusks and zoophytes which can exist only in its salt waters. The sides of the caves, as far as the highest tides swept, were studded with crimson and purple and amber mollusca, glistening like jewels in the light pouring down upon them from the eyelet-openings overhead. Not the space of a finger-tip was clear. Above them in the clefts of the rock hung fringes of delicate ferns of the most vivid green, while here and there were nooks and crevices of profound darkness, black with perpetual, unbroken shadow. I had known the caves well when I was a boy, but it was many years since I had been there. Now I was alone in them with Olivia, no other human being in sight or sound of us. I had scarcely eyes for any sight but that of her face, which had grown shy and downcast, and was generally turned away from me. She would be frightened, I thought, if I spoke to her in that lonesome place, I would wait till we were on the cliffs, in the open eye of day. She left my side for one moment while I was poking under a stone for a young pieuvre, which had darkened the little pool of water round it with its inky fluid. I heard her utter an exclamation of delight, and I gave up my pursuit instantly to learn what was giving her pleasure. She was stooping down to look beneath a low arch, not more than two feet high, and I knelt down beside her. Beyond lay a straight narrow channel of transparent water, blue from a faint reflected light, with smooth, sculptured walls of rock, clear from mollusca, rising on each side of it. Level lines of mimic waves rippled monotonously upon it, as if it was stirred by some soft wind which we could not feel. You could have peopled it with tiny boats flitting across it, or skimming lightly down it. Tears shone in Olivia's eyes. "It reminds me so of a canal in Venice," she said, in a tremulous voice. "Do you know Venice?" I asked; and the recollection of her portrait taken in Florence came to my mind. Well, by-and-by I should have a right to hear about all her wanderings. "Oh, yes!" she answered; "I spent three months there once, and this place is like it." "Was it a happy time?" I inquired, jealous of those tears. "It was a hateful time," she said, vehemently. "Don't let us talk of it. I hate to remember it. Why cannot we forget things, Dr. Martin? You, who are so clever, can tell me that." "That is simple enough," I said, smiling. "Every circumstance of our life makes a change in the substance of the brain, and, while that remains sound and in vigor, we cannot forget. To-day is being written on our brain now. You will have to remember this, Olivia."