sea-weeds may afterwards be dropped, so that the tufts may droop elegantly from the mimic cliff. A more elegant way of appropriating branching corals, is to make a broad foot of cement to them, plunging the base of the branch in it while soft; these, when the cement has hardened, will stand on the floor of the tank like trees, and imitate more perfectly the mode of growth of the arborescent madrepores.
Whenever cement is used, it will be absolutely necessary to allow it to remain in water for at least a month, in order to soak out the free lime, before it be introduced into the water which contains animals. The water in which it is soaked should be frequently changed, and as long as any prismatic scum appears on the surface, the cement is unfit for use. I have known a whole consignment of animals killed in one night from a neglect of this precaution.
The Bottom.—As very many marine animals burrow, and as the observation of their proceedings is very interesting, they should be provided with the means of gratifying their inclinations. For this purpose a layer of sand should be put on the bottom of the tank, which may vary in depth from one to three inches. If sand from a sea-beach can be readily obtained, it is the most suitable; but the next best is coarse river-sand, such as the Thames sand commonly sold at the stone-wharves of London for building purposes. It should be well washed, until the water runs away clean: fresh water will do very well for this, but it must be drained off before the sand is put in. What is called silver-sand, and the common yellow earthy sand, sold in the shops for scouring, are not at all suitable, as
