One day when we were looking into Monday Pond, Mary saw a curious object that looked more like a hollow dragon than anything else. It had all the shape and size of one of the dragons; the legs and eyes and masked face, the pads on the back that looked like half-fledged wings. But there was a transparency and emptiness about it that was uncanny and ghost-like. Then, too, when we looked more closely there was a great rent down the back. And that made the mystery plain. The real dragon, the flesh and blood and breathing live dragon, had come out of that long tear, leaving his skin behind! It was his complete skin, too, back and sides and belly, out to the tips of his feelers and down to his toes and claws. "But why should he shed his skin? Hasn't he any skin now?" asked Mary. "Of course he must have a skin. How could he keep his blood in, and what would his muscles be fastened to, for he is a boneless dragon, and his skeleton is his outside shell, with his muscles fastened to it? So how could he live at all without a skin? He must have a new skin." And, of course, that was exactly it. He had cast his old skin, as a snake does, and had got a brand-new one. Why shouldn't a dragon change his skin if a snake can? But Mary is persistent about her "whys," and I was quite ready for her next question, which came after a moment of musing. "Why should he shed his old skin and get a new one? Is the new one different; a different color or shape or something?" "No; not a different color or different shape especially, but a different size. The dragon is growing up. He is like a boy who keeps on wearing age-nine clothes until they are too short in the sleeves, too tight in the back, and too high-water in the legs. Then one day he sheds his age-nine suit and gets an age-eleven one. See?" "What a funny professor you are! Is that the way you lecture to your classes?" "Gracious, no, Mary! This is the way: As the immature dragon grows older, his constant assimilation of food tends to create a natural increase in size. But the comparative inelasticity of his chitinized cuticula prevents the actual expansion, to any considerable degree, of his body mass. Thus all the cells of the body become turgid, and altogether a great pressure is exerted outwards against the enclosing cuticular wall. This wall then suddenly splits along the longimesial line of the dorsum, and through this rent the dragon extricates itself in soft and defenceless condition, but of markedly larger size. The new cuticula, which is pale, elastic and thin at first, soon becomes thicker, strongly chitinized and dark. The old cuticle, or exuvia, which has been moulted, is curiously complete, and is a hollow or shell-like replica of the external appearance of the dragon even to the finest details. How is that, Mary?" "Very instruct--instructing"--with an effort--"indeed," replies Mary, with grave face. "But I guess I understand the change from age-nine to age-eleven clothes better."