8 ANIMAL ACTIVITIES. 
Snails and Mussels. Collect pond-snails and put 
in a vessel of water with sticks, dead leaves, and 
growing plants. Place in the bottom of 
the dish two or three inches of sand and 
introduce one or two fresh-water mussels. — 
Watch the movements of both snails and 
mussels. Find out how they breathe. 
The plants furnish food for the snails, and 
the mussels thrive without feeding, living 
Fic. 5.—A for years in an aquarium like that just de- 
Water-snail scribed. Watch for the eggs and growing 
(Planorbis). Sounge, Use directions in Chapter XV. 
Aquaria. The mussels just mentioned breathe the 
air dissolved in the water, and, on this account, fresh 
air must be supplied. There are several ways of doing 
this. The simplest method consists in furnishing 
Fic, 6.—Shell of a Fresh-water Mussel (Axodon). 
growing plants enough in the aquarium to take up 
the carbon dioxide gas exhaled by the animals, and at 
the same time to give the water a supply of oxygen. 
Such plants may be easily collected while looking for 
snails. Water-plants are also for sale at bird stores. 
