A large glass aquarium may be purchased from any School Supply Company at a cost of a few dollars, but a small globe-shaped aquarium such as is used for gold-fishes will be found suitable for school purposes. If it is not possible to secure either of these, a large glass jar, such as a battery jar or large fruit jar, will be found to answer quite well. To set up the aquarium, put into the jar about two inches of clean shore sand (sand from a sand pit, washed until the water comes away clear, will do). Secure from a pond some water-plants, place these in the jar with their roots covered with sand and secured in position by small stones. Pour in water until the jar is nearly full, taking care not to wash the roots out of place, and then put in a freshwater clam and a few water snails. These are scavengers, for the clam feeds upon organisms that float in the water, while the snails eat the green scum that grows on the glass. The other aquarium specimens may now be put in. One fish about three inches long to a gallon of water is about the right proportion. When there is a sufficient quantity of plant life to keep the water properly oxygenated and enough animal life to supply the carbon dioxide necessary to keep the plants growing well, the aquarium is said to be _balanced_. The balanced aquarium does not require that the water be changed more often than once in two months. Too much direct sunlight causes too rapid growth of green slime, hence the aquarium should not be set in a window. Close to a window through which the sun shines upon it for an hour or longer each day is the best position. Do not supply more food to the animals in the aquarium than they can eat up clean. Crayfish, perch, trout, and other freshwater fishes are destructive of insect larvae and other aquarium specimens, hence care must be taken in selecting the specimens that are put together into an aquarium. Suitable animals for the aquarium: mosquito larvae, dragon-fly larvae, caddice-fly larvae, crayfish, clam, water snails, tadpoles, fish, frog, turtle. AQUARIUM SPECIMENS MOSQUITO Time.--May or June. ~Questions and Observations.~--At what time of the year are mosquitoes most plentiful? In what localities are they most plentiful? Why are they most plentiful in these places? Are mosquitoes ever seen during fall or winter? How do you account for their rapid increase in number early in summer? How do mosquitoes find their victims? Observe the humming noise and try to discover how it is made. Watch a mosquito as it draws blood from your hand. Does the point of the beak pierce the skin? Capture a number of mosquitoes and place them in a jar containing some water and a few straws or sticks standing upright out of the water. Cover the mouth of the jar with a glass plate or fine gauze. Watch for the rafts of mosquitoes' eggs on the surface of the water.