8 THE AQUARIAN NATURALIST. 



entire superficies of these rocks speedily becomes in- 

 vested with a dense vegetable growth, itself sufficient 

 to aerate and keep in a healthy condition the entire 

 contents of the aquarium, even without the introduc- 

 tion of plants of more conspicuous character ; every 

 stone in time becomes covered with a thick and moss- 

 like carpet, from whence, in the sunshine, bubbles of 

 oxygen may be seen to stream in copious abundance, 

 and almost rendering other care unnecessary. A 

 second important use derivable from the rock-scenery 

 we are here recommending, is the provision of shelter 

 and secure retreat for such animals as may require an 

 asylum. We ought always to bear in mind, that the 

 more nearly we can imitate the usual habitat of our 

 protegees, the more successful will be our efforts to pre- 

 serve them in a healthy condition. A little reflection 

 will at once teach us, that to seek retirement and se- 

 clusion, except at certain times of the day, is with many 

 animals an imperative instinct, a law of their economy 

 that cannot be broken without producing injurious 

 effects. It is therefore desirable so to dispose our 

 materials as to leave caves and crannies and hiding- 

 places, whereunto animals requiring such protection 

 may betake themselves. 



Shade likewise is a desideratum of no trifling im- 

 portance : constant or even prolonged exposure to the 

 full glare of daylight must necessarily prove pre- 

 judicial to animals that frequent the umbrageous 

 pools, or delight in the seclusion of dimly-illuminated 

 corners of their native localities. In the construction 

 of our rock-work, therefore, this point should by no 

 means be lost sight of. 



