THE FRESH-WATER AQUARIUM. Ad 
snails breed rapidly in tanks, but the carp devour the 
young as fast as they appear; hence it is advisable to 
remove the spawn into jars containing healthy plants, such 
as Callitriche, in which they may remain for observation 
| of growth, till stout enough to be committed to the tank. 
POE 
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PLANORBIS CORNEUS, PALUDINA VIVIPARA, LYMNEA STAGNALIS, 
UNIO PICTORUM, TUMIDUS, & ANODON CYGNEUS. 
Among the bivalves, the fresh-water swan mussel, 
Anodon cygneus, and the Duck mussel, Unio pictorum, 
are interesting burrowers, and perform a great service in 
the tank. They act as scavengers, not by the process of 
eating off objectionable growths, as in the case of uni- 
valves, but by the straining off of matters held in suspen- 
a 
