RES TOR A TION OF AQ UARIA. 3 1 



remember that the secret of his successful preservation 

 of animals and plants lies in his imitating natural 

 conditions as much as possible. And a very slight 

 consideration will show him that round bell-glasses, 

 and square tanks, having three or four glass sides, are 

 as far removed from these as they well can be, unless 

 in shady places. 



It is this intensity of light which promotes the 

 rapid growth of the greenish film coating the inner 

 surfaces of the very glass through which you want to 

 watch your animals, as if it were a judgment inflicted 

 on your unscientific taste ! This is not the worst of 

 it : the same lowly-organised and rapidly-developing 

 algcg will mantle your water plants with their green 

 slime, and strangle and suffocate them in folds of 

 sickly-looking greenery. At the slightest sign of 

 anything of this kind occurring, the aquarium ought 

 to be put away from the light. A few days in a 

 darker corner will soon restore it to its healthy con- 

 ditions, if only the disease has been taken in time. 

 Another means of keeping down the excessive growth 

 of aquatic vegetation is by introducing more marsh 

 snails, such as Paludina, the larger species of Pla- 

 norbis (P. corneus\ &c. These crawl over the inner 

 surfaces of the glass and clean it, removing and de- 

 vouring the green film ; they also keep down the 

 tendency to too rapid growth in Anacharis, Callitriche, 

 &c., on account of their fondness for the young and 

 growing shoots. 



