In the aquarium we have a most convenient field for the study of Natural History: to learn the varieties, nature, names, habits, and peculiarities of those endless forms of animated existence which dwell in the hidden depths of the sea, and at the same time to improve our minds by cultivating our powers of observation. The pleasure derived from the aquarium comes from the excitement of finding and collecting specimens, as well as from watching the tank itself. There can be no more pleasant accompaniment to the sea-side walk of the casual visitor or summer resident of a watering-place, than to search for marine plants and animals among the fissures, rocks, and tide-pools of the sea-washed beach or cape. Nature is always as varied as beautiful. Thousands of strange forms sport under the shadow of the brown, waving sea-weeds, or among the delicate scarlet fronds of the dulse, which is found growing in the little ponds that the inequalities of the beach have retained. It is down among the great boulders which the Atlantic piles upon our coast, that we may find endless varieties of life to fill the aquarium, though not those more gorgeous hues which distinguish the tenants of the coral reefs on tropical shores. Yet even here Nature is absolutely infinite; and we shall find ourselves, day after day, imitating that botanist who, walking through the same path for a month, found always a new plant which had escaped his notice before. So, too, in exploring the open sea, besides the pleasure of sailing along a variegated coast, with sun and blue water, we have the constant excitement of unexpected discovery: for, as often as we pull up the dredge, some new wonder is revealed. Words fail to describe the wonders of the sea. And all that we drag from the bottom, all that we admire in the aquarium, are but a few disconnected specimens of that infinite whole which makes up their home. So, too, in watching the aquarium itself, we shall see endless repetitions of those "sea-changes" which Shakspeare sang. Ancient mythology typified the changing wonders of aquatic Nature, as well as the fickleness of the treacherous sea, in those shifting deities, Glaucus and Proteus, who tenanted the shore. The one the fancy of Ovid metamorphosed from a restless man to a fickle sea-god; the other assumed so many deceptive shapes to those who visited his cave, that his memory has been preserved in the word Protean. Such fancies well apply to a part of Nature which shifts like the sands, and ranges from the hideous Cuttle-fish and ravenous Shark to the delicate Medusa, whose graceful form and trailing tentacles float among the waving fronds of colored Algae, like "Sabrina fair, Under the glassy, cool, translucent wave, In twisted braids of lilies knitting The loose train of her amber-dropping hair." * * * * * THE YOUNG REPEALER.