Turtles and young, 202. Tusks of elephant, 124. Tussock worm, 64. Two methods of reproduction, 194. Types of insect mouth, 93. U Understanding the Bible, 281. Underwing moth, 130. V Variation and natural selection, 49. by crossing, 53. Virchow and man's ancestry, 187. Vireo's color, 115. W Wagner and isolation, 241. Wallace and evolution, 39. Warm-blooded animals, 99. Weissman and evolution, 235. Wilberforce, Bishop, and evolution, 41. Wintering of ground hog, 103. Wintering of mammals, 103. Wintering of squirrels, 103. Woodchuck, 103. Woodpecker's nest, 146. Y Young growing finer, 272. APPENDIX BIBLIOGRAPHY In connection with each chapter, wherever this is possible, there are four classes of references. First is named a small and inexpensive but satisfactory book on the subject. Second, a more comprehensive book, readily accessible and not unduly expensive. Then a few of the most satisfactory reference books on the subject independent of cost or ready availability. Fourth, a list of references to articles in the eleventh edition of the Encyclopedia Britannica. CHAPTER I. _Evolution before Darwin._ 1. -- -- -- -- 2. Biology and Its Makers, Locy. 3. From the Greeks to Darwin, Osborn. Chapters 1, 2, 3, 19. 4. Encyclopedia Britannica, 11th edition, article, _Evolution_, section, _History_. CHAPTER II. _Darwin and Wallace._ 1. The Coming of Evolution, Judd. 2. Charles Darwin, Poulton. 3. Life and Letters of Charles Darwin, by his son, Francis Darwin. 2 vols. My Life, A. R. Wallace. 2 vols. 4. Encyclopedia Britannica, articles _Darwin_, _Wallace_. CHAPTER III. _The Underlying Idea._ 1. Evolution, Geddes and Thompson. 2. The Origin of Species, Charles Darwin. 3. The Evolution Theory, Weissmann. 2 vols. 4. Encyclopedia Britannica, articles _Variation_ and _Selection_. CHAPTER IV. _Adaptation for the Individual._ 1. Colin Clout's Calendar, Grant Allen. 2. Evolution and Animal Life, Jordan and Kellogg. Chapters 16, 19. 3. Darwinism, Wallace. 4. Encyclopedia Britannica, articles _Adaptation_, _Colours of Animals_, _Hibernation_. CHAPTER V. _Adaptation for the Species._ 1. Colin Clout's Calendar, Grant Allen. 2. Evolution and Animal Life, Jordan and Kellogg. 3. Darwinism, Wallace. 4. Encyclopedia Britannica, articles, _Metamorphosis_, _Song of Birds_. CHAPTER VI. _Life in the Past._ 1. The Story of Our Continent, Shaler. 2. Elements of Geology, Blackwelder and Barrows. 3. The Story of Evolution, McCabe. 4. Encyclopedia Britannica, article, _Geology_ (palaeontological and physiographical). CHAPTER VII. _How the Mammals Developed._ 1. -- -- -- -- 2. Plant and Animal Children, Torelle. 3. -- -- -- -- 4. Encyclopedia Britannica, article, _Mammalia_. CHAPTER VIII. _The Story of the Horse._ 1. The Evolution of the Horse in America, Osborn, in _The Century_, November, 1904.