THE BOTTOM. 261 



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 madrep'ores. 



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 



