nature
and strike a balance so that the water need never be changed except
when it becomes foul or to clean the glass.

These are called "self-sustaining" aquaria and they are the only kind
to have unless we can furnish running water from a public water
supply. Self-sustaining aquaria are very simple and any boy or girl
living near a brook can stock one at no expense whatever.

The method is as follows: First cover the bottom of the aquarium with
a layer of sand and pebbles to a depth of about two inches. Then plant
in the bottom some aquatic or water plants that you have collected
from a near-by lake. Any kind of water plants will do--the kind of
plants boys always call seaweed, even a thousand miles from the sea.
In collecting the plants, choose small specimens and obtain roots and
all.

If you can find it, the best plant is fanwort. Other good kinds are
hornwort, water starwort, tape grass, water poppy, milfoil, willow
moss, and floating plants like duckweed. Even if you do not know
these by name they are probably common in your neighbourhood. Fill the
tank with clean water. That taken from a spring or well is better than
cistern water. After two or three days, when the plants seem to be
well rooted, put in your fish. You may keep your aquarium in a light
place, but always keep it out of the sun in summer and away from the
heat of a stove or radiator in winter.

The nature student will not attempt to stock up his aquarium
immediately. He should always leave room for one more fish or bug. One
year I started with a lone newt and before the summer was over I had
thirteen sunfish, pickerel, bass, minnows, catfish, carp, trout, more
newts, pollywogs or tadpoles, five kinds of frogs, an eel and all
sorts of bugs, waterbeetles and insects. I soon found that one kind of
insect would kill another and that sometimes my specimens would grow
wings over night and fly away. But to learn these things, even at our
own disappointment is "nature study." If we knew it all in advance, we
would not have much use for our experimental aquarium.

Always keep a few snails and tadpoles, for they are the scavengers and
will eat the refuse stuff and keep the glass free from greenish scum.
Boys and girls are almost sure to overfeed fish. This is a great
mistake. The best standard feed is dried ants' eggs that can be bought
for a few cents a box at any bird and fish store. Do not feed pieces
of bread and meat. Study what their natural food