NATURAL SEA- WATER. 11 



render the shores uninhabitable. The naturalist ought 

 therefore to be very cautious how he allows the 

 bottom of an old-established tank to be disturbed; 

 still more so in permitting the casual introduction of 

 any shell or stone into his aquarium that is polluted 

 with this noisome pestilence. We have ourselves lost 

 many valuable colonies owing to the imprudent zeal 

 of friends, who, in their anxiety to add some new- 

 found specimen to our stock, have neglected thoroughly 

 to cleanse the shell, or pebble upon which it was at- 

 tached, from the adherent filth. 



To procure a supply of sea-water adapted to the 

 purposes of the Aquarium is the next consideration ; 

 and simple as this part of the business may appear, it 

 is by no means always an easy matter even to parties 

 resident upon the sea-shore. On certain favoured 

 beaches, it is true, nothing more is requisite than to 

 take a watering-can to the water's edge, and fill it 

 from the brimming ocean ; but this is unfortunately 

 rather an exceptional privilege. On most of our 

 coasts, too, it generally happens, that during both the 

 advancing and receding tide, the muddy shore, stirred 

 up by the incessant turmoil of the waves, pollutes the 

 sea to such an extent that it is quite inadmissible into 

 the tank. So that the naturalist, like the poor thirst- 

 parched mariner, with 



" Water, water, all around, 

 And not a drop to drink ! " 



eyes the expanse of dirty waves in a state of hope- 

 less tantalization. In such a case, the only chance 

 is to procure a boat, and obtain, at a sufficient 



