AqUAEIUM. 



When about to assume the pupa state, the larvae fix their cases 

 Jo some sohd substance beneath the water, and close the two 

 extremities with a kind of grating which, while it excludes in- 

 trusive enemies, freely admits of the passage of water through 

 the tube, the water being required for respiration. "When nearly 

 arrived at their perfect form, they eat their way through the 

 grating with a pair of strong mandibles specially provided (or so 

 it would seem) for this one object. They then swim to th(> 

 surface and undergo then- final change in the air. 



The origioal promoters of the aquarium — ^^among whom 

 Mr. Warrington occupies a prominent place — were suddenly 

 brought to a dead stand through a difficulty they had not 

 anticipated. As the older leaves of the plants decayed, a green 

 scum began to settle on the surface of the water and on the 

 sides of the tank, shrouding the carefuUy-nurtured specimens 

 of animal and vegetable hfe with an ugly veil. In the hands 

 of a man of less thought and patience than Mr. Warrington, 

 the obstacle would have been regarded as insuperable, and the 

 whole project abandoned. It occurred, however, to the acute 

 experimentalist to enlist the services of certain of the moUusca, 

 whose nature it is to possess an appetite for just the sort of 

 garbage that bade fair to nip the aquarium notion in the bud. 

 The large number of these scavengers afford a wide field for 

 selection ; but some care must be used in selecting such of 

 them as really prefer the confervm, or vegetable decay, and not 

 the vegetables themselves, otherwise you will not be able to 

 keep a decent plant in the tank. Bear in mind, too, that it 

 is very easy to overstock the aquarium with these rubbish- 

 consumers ; although they may prefer garbage, you may depend 

 they will not allow respect for your choice plants to stand in 

 the way of their hunger. It is next to impossible, however, to 

 give exact directions as to the number of scavengers your 

 tank should contain ; nothing but experience wiU enable you 

 to arrive at a correct balance. 



Among the most suited to the purpose are the Paludina, or 

 Fresh-water Winkle, and the Planor- 

 bis, or Trumpet-snail. The last is an 

 inhabitant of most ponds and ditches, 

 and may therefore be easily obtained, 

 as may the former. The Helix horn- 

 hex is a smaller species of fresh-wator 

 THE TRUMPET-SNAIL. snail, but is very usetul as a purifier 

 of the aquarium ; &om the smallness of its size, it j% perhaps, 



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