Use a piece of seasoned white wood 1¼ inches thick for the bottom. If you wish your aquarium to be, say, 16 inches wide and 30 inches long, this bottom board should be 20 x 34 to give a margin at the edge. The size of a home-made aquarium can be anything that you desire. It is customary to allow a gallon of water to each three-inch gold fish that will inhabit it. By multiplying the three dimensions, length, width and height of your box and by dividing your result, which will be in cubic inches, by 231 (the number of cubic inches in a gallon) you can tell how many gallons of water it will hold. Of course the rule for gold fish is not absolute. The nature student will probably have no gold fish at all. They are not nearly so interesting as our native kinds. Besides nearly all varieties of fresh water fish will either kill gold fish or if they are too large to kill will at least make life so miserable for them that to keep them together is cruelty to animals. If we keep in our aquarium the specimens that we collect in our neighbourhood, beetles, newts, crawfish, snails, and tiny sunfish the number may be greatly increased. Overcrowding however is very bad. The ideal we should strive for is not “how many specimens” but “how many kinds” we can have in our collection. The white wood board should have three or four hardwood cleats screwed to the bottom to prevent warping. The corner pieces of our glass box may either be made of sheet copper or heavy tin, or of wood, if we cannot work in metals. The wooden strips and the bottom board should have grooves ploughed in them to hold the glass. All the woodwork should be given several coats of asphalt varnish and to further waterproof it and as a final coat use some kind of marine copper paint that is used to coat the bottoms of vessels. Never use the common white lead and linseed oil paint for an aquarium. You can sometimes buy aquarium cement or prepared putty at a “gold fish” store. This you will need to putty in the glass. If you cannot buy it, make it yourself from the asphalt varnish and whiting. Be sure that the paint and putty of an aquarium is thoroughly dry before you fill it with water. Perhaps the most satisfactory way to study fish and insect life in water is to use all glass boxes and globes. So many kinds of fish and insects are natural enemies, even though they inhabit the same streams, that they must be kept separate anyway. To put them in the same aquarium would be like caging up two game roosters. If we were studying the development of mosquitoes, for instance, from the larvae or eggs to the fully developed insect, we should not get very far in our nature study if we put them in an aquarium with fish. A fish will soon make short work of a hundred mosquito wigglers just as a large frog will eat the fish, a snake will eat the frog and so on.