Day by day the water grew clearer and clearer, until, at the end of three weeks, it was beautifully translucent. Three more weeks passed, during which the beauty of the Aquarium was much heightened by a luxuriant growth of Confervae mingled with Enteromorpha, which together covered all those parts of the stones which received a direct light. The mimic rocks seemed draped in green velvet, and in the sunlight were studded with pearly bubbles. There was, however, one blemish: the hungry crabs had so nibbled the larger plants that it was deemed necessary to renew them, in order to secure a sufficient supply of food and oxygen. Accordingly, a fine specimen of Enteromorpha was added. It consisted of five or six delicate fronds about five inches in length, and these soon increased to treble their original number and twice their original size. At the end of about two weeks, they suddenly became covered with a dull bluish mould, at the same time ceasing to give out bubbles; and the whole plant, instead of rising to the surface of the water as hitherto, hung limp from the fissure where it was placed, and trailed upon the sand. Coincidently, (was it consequently?) a greenish tinge pervaded the water, speedily increasing in depth and opacity. In five days, no object could be discerned six inches from the glass, and my beautiful Aquarium was transformed to an unsightly ditch. Yet the water was apparently pure, and the activity of its inhabitants was in no wise lessened. What was this vexatious greenness? Was it animal or vegetable? Was it the diffused spores of the perfected Enteromorpha or of the rank Confervae upon the stones? If neither, what was its cause? Excess of light was the most obvious suggestion; and so it was supposed that its exclusion might be a potent remedy. Therefore a double curtain of glazed muslin was stretched across the window; and the tank, both top and sides, wrapped in folds of paper. A week of darkness changed the deep green to a dingy olive. But the experiment could not be continued. The nightly admission of air by lifting the paper covering was insufficient to maintain the imprisoned creatures. They were happy, though captive, while in a mimic ocean, but miserable in a dark dungeon. Languid and spiritless, they lay supine, or crawled listlessly and aimlessly about. This would not do, and so light was again admitted freely to all but one side of the tank; there, a screen of yellow paper intercepted the direct rays of the sun, while upon the top they fell through the foliage of a Clematis vine. Three weeks more wrought a slight change for the better; but it was too slight and too slow for my patience, or that of curious friends waiting to see my Aquarium. The second experiment had failed, and so once more the tank was emptied. Two or three animals only had died; all the others gave evidence of health. Again they were removed to other vessels, and again I began anew.