12 THE BOTTOM. 



animals. The water in whicli it is soaked should 

 be frequently changed, and as long as any pris- 

 matic 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 they will tinge the water after any 

 amount of washing, the former with lime, the latter 

 with ochre. 



Small pebbles or fine gravel, likewise well 

 washed, may be used to vary the bottom with the 

 sand. 



Masses of rock, of dimensions suitable to the 

 Aquarium, should be put in to aiford shelter and 

 concealment to such animals as like the gloom. 

 To afibrd this in the highest degree, a flat piece 

 may be set, like a table, or cromlech^ upon two or 

 three upright blocks ; or two tall pieces may lean 

 against each other, forming a rude arch; — care 



