THOUGH the principle of protective resemblance, as explained in the last chapter, will account for the colours and markings of those butterflies which imitate the _Heliconidæ_, it does not explain how the _Heliconidæ_ themselves came to be as they are; for in nature every mark and line and shade has a meaning, and has come into existence by virtue of some law or another. Beauty itself, independently of any _arrière pensée_, as we may call it—remembering those flower-resembling spiders—requires to be explained. Nor are the _Heliconidæ_ themselves, though gaudily dressed showy butterflies, anything like so beautiful as many others; for instance, as the _Morphos_, those giants of their kind, who sweep like stars through the tropical forests on wings whose whole broad surface is blue, but a blue that flashes like a drawn sword and has a hundred glints and gleamings of ever-varying light. High-fliers they are for the most part, keeping to the tops of the trees, but every morning, and always at the same time, they make a descent into the glades and alleys of the forest, where for a little they flap lazily backwards and forwards, now in eclipse, now flashing forth into sunlight, as though to flaunt their beauties in the face of the lower world. Such openings in the primeval forest are often made by the fall of great trees—for even where the axe is not there is death in the midst of life—and as these majestic insects sail high above them in a world of air and light, their shadows fall upon the place beneath, and trace their course along the ground. When the sun’s rays strike into them, such clearings become the gathering grounds of various butterflies. Besides the great _Morphos_, the flashing of whose wings in the sunlight can be seen sometimes a quarter of a mile away,[112] various species of _Heliconeas_—the one we have just been reading about—whose black wings are in some species spotted with scarlet, in others with white or blue, waltz about the bushes or undergrowth, “dancing in the chequered shade”; fritillaries somewhat like our own, but of larger size and more effective colouring, fly higher up, about the tree-trunks, whilst over the ground itself, carpeted as it often is with flowers fallen from the leafy world above, and scenting the air, ghost-like butterflies, whose clear, transparent wings are without any colouring matter, ceaselessly hover and flit.