It is among the rock‐tide pools that some of the most prized treasures of the aquarium may be obtained. There are the little shrubberies of pink coralline, Southey’s “arborets of jointed stone”; there are the crimson banana‐leaves of the _Delesseria_, the purple tufts of Polysiphoniæ and Ceramia, the broad emerald green leaves of _Ulva_, and the wavy, feathery _Ptitola_ and _Dasya_. Then everywhere is to be found the lovely _Chondrus crispus_, with its expanding fan‐shaped fronds cut into segments, every segment of every frond reflecting a lovely iridescent azure. [Illustration: DELESSERIA.] [Illustration: ULVA.] Mr. Gosse was reclining one evening on the turf, looking down on a Devonshire cove that formed the extremity of a great cavern. Though it was low tide, the sea did not recede sufficiently to admit of any access to the cove from the shore. Presently he saw a large rat come deliberately foraging down to the water’s edge, peep under every stone, go hither and thither very methodically, pass into the crevices, exploring them in succession. At length he came out of a hole in the rock, with some white object in his mouth as big as a walnut, and ran slowly off with it by a way the observer had not seen him go before, till he could follow him no longer with his eyes because of the projections of the precipice. What could he possibly have found? He evidently knew what he was about. From his retirement into the cavern, when the sea had quite insulated it, the sagacious little animal had doubtless his retreat in its recesses, far up, of course, out of the reach of the sea, where he would be snugly lodged when the waves dashed and broke wildly through the cove, kindling millions of fitful lamps among the clustering polypes below. The influx of the tide is frequently, as we all know, very rapid on the sands, and cuts off the communication between rocky islets and the shore in rather a treacherous fashion. Mr. Gosse, in giving an account of such influx on a part of the Devonshire coast says:—