able cleaners, the pity is, that they will not see what is required of them, and do that only.
Again, the univalve mollusks do not keep the sides so clean, but that an occasional cleansing of another kind is sometimes necessary, and if the aquarian is not disposed to keep an army of quite semi-efficient scavengers, the remedy will be found in an occasional cleansing of the sides, by means of a sponge attached to a stick, which must be plied over the whole surface, and occasionally taken out and washed in clean water, to remove the green scum, that it soon gets covered with.
Use of Confervoid Growths.—But I should object to any frenzy about cleansing tanks. As I said at starting, they should be self-supporting, and if Planorbis or Paludinæ are used in the proportion of about four of each to every gallon of water, a good view will always be preserved with the use, now and then, of the sponge alone.
Periodical Cleansing.—When a tank has stood twelve-months or more, the water not having been changed at all during the whole time, it may be necessary to turn out the contents and re-stock it. This is not to be done unless the bottom has become black, and the roots of the plants show signs of decay, in fact, not unless it really wants it, and if bottomed with mould it certainly will, and it must be done accordingly. The live stock should be removed by means of a hand-net, the water drawn off by means of a syphon of glass, or gutta percha, and the plants taken out carefully and put by themselves, and then after removing
