gold-fish and snails.

[Illustration: SNAILS.]

I have given drawings of the two best kinds of snails. One is shown with
its broad foot expanded, by which it moves along the surface of the
water, or on the glass when eating the green coating spoken of. Snails
also eat decaying vegetable matter.

For keeping the water very clear, introduce a small-sized fresh-water
mussel. Give him at least two inches of sand, in depth, in a corner of
the tank, to burrow in, but watch him well, for if he dies without your
knowledge your aquarium will be ruined.

[Illustration: CADDIS-WORMS.]

In the illustration are figured three kinds of caddis-worms. These worms
are useful for consuming decaying animal matter. When a "cad" has grown
too large for his house, he makes a little case of silk, which he covers
at each end with pieces of leaves, wood, or straw, biting them to the
right length; some fasten on small bits of stone and shells. However
rough the outsides of their houses may be, the insides are smooth, and
lined with silk. When he changes into a chrysalis, he crawls up a plant,
and closes up both ends of his house with a strong net-work of silk,
which allows the water to pass through, but prevents the entrance of
enemies. As he has taken care to place himself near the surface of the
water, he easily escapes when he comes forth a four-winged insect
resembling a small moth.

[Illustration: APPLE-SMELLERS.]

Apple-smellers, or merry-go-rounds, are very interesting. They are of an
intense shining black in color, and generally school together, moving in
circles, with great rapidity, on the surface of the water. They are
called apple-smellers on account of the strong odor they possess,
resembling that of apples or quinces, and merry-go-rounds on account of
their merry circling motions around one another. Young apple-smellers
live on the bottoms of ponds, and look like centipedes. When the time
comes for them to change into real apple-smellers, they climb up a
plant, and make small bags of gray paper, into which they fasten
themselves till they get their swimming legs and shining black new
clothes, after which they burst open the paper bags, and swim off to
join their friends gliding so merrily on the surface of the pond. When
an apple-smeller dives to the bottom of a pond to take a rest or to
feed, he attaches a globule of air to his tail (see cut); this he
breathes while under water.

[Illustration: STICKLEBACKS.]

The nine