FRESH- WATEK AQUARIA. 21 



must be kept (.roperly emhcilded unions' tliu stoiicH at the bottom. I 

 have kept Nitella for two years without it having at auy time had its 

 roots embedded. 



I have always fouud my aquaria do best wheu placed before a 

 window where they may have the direct rays of the suu for a good part 

 of the day ; the plants arc thereby induced to grow vigorously, and 

 these and the pieces of rock afford ample shade for those animals that 

 require it. However, if it is not convenient to have it in such a posi- 

 tion, any other will do, provided a fair amount of light can get to it. 

 There may be, nevertheless, a disadvantage in an excess of direct 

 sunlight. It causes the glass sides of the vessel to become covered 

 with confer void growth, which, although useful both as food stuff 

 and for the evolution of oxygen, considerably obstructs the view 

 through the glass, a desideratum, especially if a tank microscope is 

 one of the possessions of the proprietor of the aquarium. 



Water should be added from time to time to replace what has been 

 lost by evaporation and other causes, so as to keep the level about 

 constant. Dead animals should be removed, but decaying water 

 plants, though somewhat u isightly, are such excellent harbour and 

 food for microscopic creatures that they should rather be introduced 

 than removed. 



Occasionally, say once a year, in the late autumn or early spring, 

 it is well to have a thorough clean out. At these times all the live 

 stock which it is wished to preserve must be taken out, as also the 

 pieces of rock and plants, and so much of the water as can be taken 

 out in a clear state, drawn off with a syphon or otherwise carefully 

 removed into another vessel, so that it may be returned to the tank 

 together with the animals, plants, and stones after the cleaning 

 process has been gone through. The reason for this is that there will 

 probably be many germs in it, besides entomostraca, rotifers, and 

 other small organisms which it is desirable to retain. The whole of 

 the gravel and grit must be taken out and thoroughly washed. An 

 enormous quantity of dirt will be found mixed up with the stones. 

 This is chiefly the effete matter which, falling to the bottom, is 

 hidden among them^indeed, this is one of the uses they subserve. If 

 there are auy snail eggs, vorticella, or other treasures attached to the 

 glass, they should be carefully stripped off, and although they cannot 

 be replaced in their original positions, they will, if returned to their 

 renovated home, continue to develop or form new colonies, as the case 

 may be. The glass, if there is any coufervse on it, should be well 

 scrubbed with soap and warm water, taking care that all the sand and 

 grit is removed, otherwise there will be most likely a number of un- 

 desirable scratches to be seen upon it. 



In such an aquarium as has been described, almost any creature 

 that inhabits fresh-water can be kept in health with little trouble, 

 provided over -crowding does not take place ; but due care must be 

 exercised in the selection of its inhabitants. For instance, it will not 

 be wise to place lish in it, if it is wished to preserve minute forms of 



