"Well, these young May-flies--the ones that don't get eaten by dragons, stone-flies, water-tigers, and other May-flies--grow larger slowly, and wing-pads begin to grow on their backs. In a year, maybe, or two years for some kinds, they are ready for their great change. And this comes very suddenly. Some late afternoon or early evening thousands of young May-flies of the same kind, living in the same lake or river, swim up to the surface of the water, and, after resting there a few moments, suddenly split their skin along the back of the head and perhaps a little way farther along the back, and like a flash squirm out of this old skin, spread out their gauzy wings and fly away. They do this so quickly that your eye can hardly follow the performance." "And then they all fly to the light and begin their dance of death," breaks in Mary. "No, wait; they are not yet quite ready for that. First, they do a very unusual thing; something that no other kinds of insects have ever been seen to do. This is it: They fly away to a plant or bush or tree at the water's edge, and there they cling for a little while and then cast their skin again." "The new skin they have just got, with the wings and everything?" asks Mary. "Exactly; the new skin. It comes off of the wings, off of the long tails and the short feelers, and all the rest of the body. No other kind of insect but the May-fly casts its skin once its wings are outspread. But now the May-fly is ready for its dizzy dance. And as it has only a few hours to do it in, it usually starts as soon as there are any lights to dance about. Think of it, to come up from under the water, get your wings and be a real May-fly, not just a crawling thing on the bottom of a pond, and have only one evening to live in! Probably to dance the whole evening through is about the best thing to do under such circumstances." "Don't any of the poor May-flies live for more than one evening?" asks Mary. "It does seem a shame to put in so long a time, one year, two years for some, getting ready to fly and then have only one evening or night for flying." "Well, yes, some do, Mary. That is, there are many different kinds of May-flies; some large ones, some small ones, some kinds with four wings, some kinds with only two, and the length of the flying time is not the same for all these kinds. Some live a day, some two, some perhaps even three or four. But there are several kinds whose flying life is just a few hours; they are born, that is, as flying creatures, after sundown and they die before the next sunrise. The first kind of May-fly whose life was ever carefully studied--this was nearly two hundred and fifty years ago, by a famous naturalist of Holland--lives only five hours after it comes from the water. But remember what a fine long time they have being young! If we could be young--but there, that's foolish. Mary, the chimes in the tower-clock are sounding. Listen!"