46 THE FRESH-WATER AQUARIUM. 
sion in the water, and filtering it in a pure state, by the 
mechanism of their syphons, and ciliated gills. It is very 
interesting to watch them thus engaged, and to note 
the force of the stream which they project from time to 
time. 
The only creature of the insect kind that I can recom- 
mend for general adoption is the caddis worm, a comical 
and interesting creature, that can never mar the beauty 
of the tank. MHalf-a-dozen may be thrown in, and 
searched for occasionally—the search will always be well 
rewarded. When the cad closes his hybernacle, it will be 
desirable to remove it to a jar, to obtain a better oppor- 
tunity of witnessing the transformation of the dormant 
worm into a four-winged fly of Stephens’s family of 
Phryganea. 
CHAPTER VIL. 
SELECTION OF STOCK. 
THE first thing to guard against is over-stocking, the 
common error of all beginners; taking large fish with 
small, I think about two or three to every gallon of water 
is the utmost that should be attempted. For a vessel of 
twelve gallons, I should recommend the following, as 
giving great variety, with considerable safety :—Six Prus- 
sian carp, of various sizes, one at least of five inches in 
length; two small Crucian carp; two small perch; two 
small loach ; two tench, of five or six inches; six or eight 
minnows; one small eel; a dozen Planorbis corneus; 
half-a-dozen Paludina vivipara; three or four fresh-water 
mussels and a dozen of different sorts of newts. 
