CHAPTER Y. 
I 
j/5 
% 
^ THE M0LLTJSCA AND THE PISH * 
hen the plants are well established, 
^ lc wa ^ er rL0 ^ forming the slightest 
scum, and the tank furnished with 
^ iree or four common Pond Snails to 
consume any decaying vegetation 
ma y occur, and keep down the 
• growth of the confervse which would 
cover the glass, and render the spectacle of its 
inmates imperfect, then the Aquarium is ready for 
the reception of the fish; which, from their grace¬ 
ful forms and agile and pleasing movements, are 
always the greatest favourites. 
Previously to describing the fish most suitable for 
our purpose, we may derive some entertainment and 
instruction from the examination of the family of 
shell-hearing mollusca of our fresh waters, whose ser¬ 
vices as scavengers are so important in the circle of 
compensating principles, upon which the establish¬ 
ment of the Aquarium is founded. The common Pond 
46 
