[Illustration: _Fig. 75. The life history of a dragon-fly as seen in an aquarium._] The transformation of one of these young insects into an adult is one of the most interesting observation lessons that can be imagined for a warm spring morning. If a dragon-fly nymph should signify its intention of changing its form in my school-room, I should certainly suspend all ordinary work and attend to him alone. Each child should see if possible this wonderful transfiguration. Floating in the water of a pond or stream one may find a little bundle of grass or weed stems, with perhaps a tiny pebble clinging to the mass. Close examination will prove this to be the "house-boat" of one of our insect neighbors, the caddice-worm. Contrasting strangely with the untidy exterior is the neat interior, with its lining of delicate silk, so smooth that the soft-bodied creature which lives inside is safe from injury. The commonest of the many forms of houses found here are those illustrated in Figs. 76 and 77. These will find all they wish to eat in a well-stocked aquarium. When full grown they will leave the water as winged creatures, like Fig. 78, and return to its depths no more. [Illustration: _Fig. 76. Case of caddice-worm._] [Illustration: _Fig. 77. Another caddice-worm case._] [Illustration: _Fig. 78. Caddice-fly._] There is surely no lack of material furnished by Mother Nature for the study of aquatic life. Every one who really believes in its usefulness can have an aquarium, and will feel well repaid for the time and effort required when the renewed interest in nature is witnessed which this close contact with living beings brings to every student. Let us take hold with a will, overcome the difficulties in the way, and teacher and pupils become students together. LEAFLET XIII. A STUDY OF FISHES.[17] BY H. D. REED. [17] Nature-Study Quarterly, No. 8: Leaflet 21. January, 1901. [Illustration] The first forms of animal life which attract the young naturalist's attention are doubtless the birds. These are most interesting to him because of their beautiful colors, their sweet songs, and the grace with which they fly. But who has watched the fishes in a brook or an aquarium and is not able to grant them a place, in beauty, grace and delicate coloration, equal to the birds? To be sure, fishes cannot sing, yet there are so many other interesting facts in connection with their habits and life-histories that it fully makes up for their lack of voice. THE PARTS OF A FISH.