For those who live in cities, a convenient place to begin the study of fishes is in the fish-market. Here we may learn to know the common food-fishes by name, and to know many interesting things about them. If there is a Public Aquarium or a Natural History Museum in your city, you can use it in connection with the fish-market. Especially valuable in Museums are the habitat groups of fishes, that is, those in which the fishes are shown in their natural surroundings. But, best of all, the place to study fishes, as is true of all other animals, is out-of-doors in their native haunts. With your dip-net or hook and line, catch the fish, and then by the aid of one of the books listed below find out what its name is. Then, by observation of the fish see what is interesting in its life-history. Find out where the mother-fish lays her eggs. Does either parents guard them? Has the fish any natural weapons of defense? If so, what are they? Does either parent care for the young 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.