Since, therefore, these forms are growing rarer every century, and some of them, such as the Dodo, Epyornis, and Moa among birds, and the northern sea-cow or Rhytina among milk-givers, have already disappeared since the times of history, we must endeavour, before others are gone for ever, to study their structure and their habits. For we are fast learning that it is only by catching at these links in nature’s chain that we can hope to unravel the history of life upon the earth. At one time naturalists never even thought that there was anything to unravel, for they looked upon the animal kingdom as upon a building put together brick by brick, each in its place from the beginning. To them, therefore, the fact that a fish’s fin, a bird’s wing, a horse’s leg, a man’s arm and hand, and the flipper of a whale, were all somewhat akin, had no other meaning than that they seemed to have been formed upon the same plan; and when it became certain that different kinds of animals had appeared from time to time upon the earth, the naturalists of fifty years ago could have no grander conception than that new creatures were separately made (they scarcely asked themselves how) and put into the world as they were wanted. But a higher and better explanation was soon to be found, for there was growing up among us the greatest naturalist and thinker of our day, that patient lover and searcher after truth, Charles Darwin, whose genius and earnest labours opened our eyes gradually to a conception so deep, so true, and so grand, that side by side with it the idea of making an animal from time to time, as a sculptor makes a model of clay, seems too weak and paltry ever to have been attributed to an Almighty Power. By means of the facts collected by our great countryman and the careful conclusions which he drew from them, we have learned to see that there has been a gradual unfolding of life upon the globe, just as a plant unfolds first the seed-leaves, then the stem, then the leaves, then the bud, the flower, and the fruit; so that though each part has its own beauties and its own appointed work, we cannot say that any stands alone, or could exist without the whole. Surely then Natural History acquires quite a new charm for us when we see that our task is to study among living forms, and among the remains of those that are gone, what has been the education and the development of all the different branches, so as to lead to the greatest amount of widespreading life upon the globe, each having its own duty to perform. With the great thought before us that every bone, every hair, every small peculiarity, every tint of colour, has its meaning, and has, or has had, its use in the life of each animal or those that have gone before it, a lifelong study even can never weary us in thus tracing out the working of Nature’s laws, which are but the expression to us of the mind of the great Creator.