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 EVOLUTION OP BIRDS. 15 modified forms, is accepted by most naturalists. As originally presented, it assumed that the continued exist- ence of any animal depended upon its adaptation to its manner of life. Among a large number of individuals there is much variation in size, form, and color. Some of these variations might prove favorable, others unfa- vorable. Those which were favorable would give to the individual possessing them an advantage over its fellows, and, by what is termed Natural Selection, it would be preserved and its favorable characters transmitted to its descendants. But the less fortunate individuals, which lacked the favorable variation, would be handicapped in the race for life and be less likely to survive. Without necessarily opposing this theory, the follow- ers of Darwin's predecessor, Lamarck, attach more im- portance to the direct action of environment on the ani- mal — that is, the influence of climate, food, and habit. The eiiect of the first two I will speak of in treating of color ; the last we may use to illustrate the difference in these two theories by asking the question, " Is habit due to structure, or is structure the result of habit ? " Has Nature, acting through natural selection, preserved those variations which would best fit a bird to occupy its place in the world, and are its habits the outcome of the characters thus acquired, or have the changes which during the ages have occurred in a bird's home, forcing it to alter its habits, been followed by some consequent change in structure, the result of use or of disuse ? For my part, I answer " Yes " to both questions, and turn to our stiff-tailed, spear-tongued Woodpecker to explain my reply. I can readily understand how the shape of these tail-feathers is the result of habit, for the same or similar structure exists among many birds having no close relationship to one another, but all of which agree in their peculiar use of the tail as a prop ; the Creep-