Of course you know that if you catch a butterfly, and let it go again, your fingers are covered with a kind of mealy dust. And if you look at a little of this dust through a microscope you will find that it is made up of thousands and thousands of the smallest possible scales, all most beautifully chiselled and sculptured, and each with a slender little stalk at the base. And if you look at a piece of the butterfly’s wings through the microscope, you will see that these scales are arranged upon it in rows, which overlap one another just like the slates on the roof of a house.