 The wings of these little animals account for what is most admirable in them. Each butterfly has four wings; their wings are so well coordinated that it seems the butterflies have only two wings when we watch them flying. Their structure is marvelous. They are made of a kind of cartilage…which colors the wings of these little animals. It makes them appear thin and transparent, like a fine piece of parchment or like a very dry and very clear stroke of the brush. [EM, 2: 309] 