THE AQUARIUM. 10 



management, if not the invention of the Aquarium is owing, 

 found, that after a time the plants in the ordinary course 

 of nature died, and the fish refusing to cat them when 

 dead, they began to decompose and so foul the water. At 

 a loss what to do to stop the ravages of disease among his 

 pets, he was driven to search in the book of nature — in its 

 broad pages, the ponds and rivers — and find out how an 

 all-wise Providence had provided for such an emergency. 

 He threw a net and brought up from the bottom of a 

 pond many dead and decomposing leaves, and to them 

 were attached, busily at work in eating them, numerous 

 little water-snails, nature's physicians. It is said that he 

 was so overjoyed at the discovery, that he burst into tears ; 

 but this did not hinder him from securing a quantity of 

 snails, and placing them in his tank, where, in a day or 

 two, the water became perfectly clear, and remained so. 



This, then, is the great secret of the Aquarium: the 

 plants supply the animals with the oxygen they need ; the 

 animals supply the plants with carbon ; and the snails and 

 other scavengers — for there arc others used in the Aquarium, 

 as we shall sec further on — remove vegetable matter, which 

 would otherwise decay and destroy the animals. 



In the Aquariuvi the snails are called to perform another 

 duty that their former life has not prepared them for, but 

 for which they are admirably adapted, and that is, cleaniug 

 the glass sides of the tank and keeping them so bright 

 that nothing shall obstruct our view of its inhabitants. In 

 time, the glass becomes covered with a deposit of minute 

 plants, which belong to a class called conferva. Between 

 their branches there exists a little world of microscopic 



