We want scavengers to clear away the superfluous vegetation, and we find them in the periwinkles which we see attached by their foot-stalk to the glass. These little mollusca do their work well: Mr. Gosse, who has watched them feeding with a pocket-glass, perceived that their saw-like tongues moved backwards and forwards with a crescentic motion, and thus, as the animal advances, he leaves a slight swathe-like mark upon the glass, as the mower does upon the field. But it is clear that there are not enough labourers in the tank we are inspecting to accomplish their task, as the lobster, who comes straggling over the stones in such an ungainly manner, is more like a moving salad than any living thing, so thickly are back, tail, feelers, and claws, infested with a dense vegetable growth. A few more black mowers are imperatively called for. The fish, the weed, and the mollusc having secured to us a clear view of the inhabitants of the tank, let us inspect them one by one. Here we see the parasitic anemone. Like the old man of the sea, it fixes itself upon some poor Sinbad in the shape of a whelk, and rides about at its ease in search of food. Another interesting variety of this zoophyte is the plumose sea-anemone, a more stay-at-home animal, which generally fixes itself upon a flat rock or an oyster-shell, and waits for the food to come to it, as your London housewife expects the butcher and baker to call in the morning. The pure white body of the neighbouring actinia renders it more observable. Its tentacles, displayed in plumes over the central mouth, which is marked with yellow, give it the exact appearance of a chrysanthemum, and should be much in favour with the mermaids to adorn their hair. A still more extraordinary creature is the _Tabella ventilabrum_. The tube of this strange animal is perfectly straight, and its large brown silk-like radiating fans, whilst in search of food, revolve just as the old-fashioned whirling ventilators did in our windows. The instant this fan is touched it is retracted into the tube, the ends just appearing outside, and giving it the appearance of a camel's-hair brush.