"It is interesting," says Mr. Gosse, "to watch the business-like way in which the Periwinkle feeds. At very regular intervals, the proboscis, a tube with thick fleshy walls, is rapidly turned inside out to a certain extent, until a surface is brought into contact with the glass having a silky lustre; this is the tongue; it is moved with a short sweep, and then the tubular proboscis infolds its walls again, the tongue disappearing, and every filament of Conferva being carried up into the interior, from the little area which had been swept. The next instant, the foot meanwhile having made a small advance, the proboscis unfolds again, the makes another sweep, and again the whole is withdrawn; and this proceeds with great regularity. I can compare the action to nothing so well as to the manner in which the tongue of an ox licks up the grass of the field, or to the action of the mower cutting swath after swath." Of Crustacea, the Prawns and the smaller kinds of Crabs may be admitted to the aquarium, though but sparingly. They are rude, noisy, quarrelsome, and somewhat destructive,--but, for the same reason, amusing tenants of the tank. All are familiar with the mode in which the Soldier or Hermit Crab takes possession of and lives in the shells of Whelks and Snails. Poorly protected behind by Nature, the homeless crab wanders about seeking a lodging. Presently he meets with an empty shell, and, after probing it carefully with his claw to be sure it is not tenanted, he pops into it back foremost in a twinkling, and settles himself in his new house. Often, too, he may be seen balancing the conveniences of the one he is in and of another vacant lodging he has found in his travels; and he even ventures out of his own, and into the other, and back again, before being satisfied as to their respective merits. In all these manoeuvres, as well as in his daily battles with his brethren, he is one of the drollest of creatures. As we advance in our practice with the aquarium we may venture to introduce more delicate lodgers. Such are the beautiful family of the _Annelidae_: the _Serpula_, in his dirty house; and the _Terebella_, most ancient of masons, who lays the walls of his home in water-proof cement.