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and pebbles laid on thickly, as many fishes, Crustaceans, Molluscs, and other creatures love to burrow in it, and besides, it contains a host of minute atoms which will afford sustenance to some one or the other of our pets;—this layer having well settled down, now comes a matter involving much taste,—the formation of rockwork,—not such fantastical grottoes as we have observed in some Cockney Aquaria, but certain nooks and crannies wherein those which delight in seclusion may ensconce themselves. The shore at Geelong affords abundant material in densely clustered masses of Serpulæ adhering to the stones, fragments of which may easily be detached with a good hammer such as we have already described,—this, while ornamental, adds thousands of interesting and graceful inhabitants, whose elegantly fringed cilias will be protruded the moment they feel the water, and about St. Kilda and similar places along the coast, scarcely a stone can be taken up that is not covered with the lovely Lepralia or Sea-scurf, minute eggs, &c., so it will only require prudent arrangement, without crowding, which in a tank of small dimensions is undesirable, as not only does it render the detection of dead or dying animals a matter of difficulty, but by displacing a certain portion of water, the animals are to some extent robbed of the means by which they should be supported.
When the tank is covered by one of the elegant domed lids which we have occasionally seen, and which we recommend to exclude dust, and to preclude the escape of such creatures as, like ourselves, are given to roaming, the rock-work as we may term it,
