g after they
are hatched? What does the fish feed upon? In what way is the fish
protectively colored? In the study of fishes, an interesting means is
the home aquarium. Any Girl Scout can easily learn how to install and
maintain a balanced aquarium, that is, one in which the water does not
have to be changed and in fact should not be changed. In such an
aquarium one may keep and study a great variety of fishes. Some of our
local fishes, such as young catfish and suckers, will prove fully as
interesting as the goldfish and many other animals besides fishes will
thrive in a small aquarium, such as tadpoles of frogs, toads, and
salamanders, adult water-newts, soft-shelled turtles, snails, and
water-beetles and nymphs of dragon-flies.

[Illustration: HAMMERHEAD SHARK

The eyes are on the ends of blunt stalks, or extensions of the sides of
the head, which suggest the name. Range: All warm seas, north to Cape
Cod.]

[Illustration: A GARDEN UNDER WATER

Starfishes, Crabs and Sea-anemones]

[Illustration: SQUID

Member of same family as Octopus, and is related to the Oyster. Has ink
bag for protection.]

Animals Without Backbones

In general the Invertebrates are animals without a backbone; that is,
they do not have an internal supporting skeleton of bone, as does the
dog or cat. Compared with mammals or birds, they are all small and some
are so very tiny that they can be seen only with a very powerful
microscope. Most of them live in the water or in the mud or sand under
the water. Hence the best place to get acquainted with them is along the
seashore or near some lake or stream.

There are several different groups of Invertebrates and between these
groups there are greater differences of structure than there is between
a horse and a hummingbird. The principal groups are:

1. The Protozoa, or one-celled animals (nearly all microscopic).

2. The Sponges.

3. The Jellyfishes, Sea-anemones, and Corals.

4. Worms of several groups.

5. Starfishes, Sea-urchins, and Sea-cucumbers.

6. Segmented Worms.

7. Crabs, Lobsters, etc.

8. Oysters, Snails, and Octopi.

9. Insects and Spiders.

[Illustration: SNAILS AND THEIR TRACKS ON THE BEACH

--_Photograph by Mary C. Dickerson._]

Seashore Life

Because of their connection with our industries or our food supply, some
of the Invertebrates are familiar to all; for instance, sponges,
corals, starfishes, crabs, shrimps, lobsters, clams, and oysters. Others