HOW TO COLLECT, AND STOCK THE TANK. 175 



advisable, as this matter is so arbitrary, for me to 

 state how my own is mapped out, leaving it to my 

 readers to imitate my arrangement or adopt a style of 

 their own as they may think proper. 



I always had, until lately, a penchant for placing 

 about two inches of sand at the bottom of the tank, 

 from the idea that it would be obliging the Fiddler- 

 crabs and their crustaceous friends. I now find 

 this is quite unnecessary. The crabs can hide under 

 stones if they like, or make themselves at home, and 

 walk about the grounds in a free and easy style. The 

 fact is that, in aerating the water, it frequently stirs 

 up the sand ; and when this is the case, it settles on 

 weeds and other objects, making them look rather 

 unsightly. I therefore now only place a few milk- 

 white pebbles and shells at the base of the vessel ; 

 around the outward edge I dispose the pieces of 

 rock that have the various delicate weeds attached. 

 These, rising up against the sides of the tank, have, 

 to my eye, a charming effect. Sometimes I place in 

 it temporary pieces of rock, and on these I lay two or 

 three mussels. When the latter have moored them- 

 selves to the glass by their silken cables, I take away 

 the pieces of rock from below. The animals then 

 live suspended as long as I please. On the pebbles I 

 lay Pholades, in such a position that I can easily 

 watch their movements. In the centre of the Aqua- 

 rium I have a large oblong piece of sandstone, that 

 projects always two inches above the top of the water, 

 in order that the fishes can get air easily, if required, 



