Great vagueness regarding the meaning of evolution, 346. Causes for this, 346. The confusion of Darwinism with organic evolution, 347. The idea that the doctrine is losing ground, 347. Scientific controversies on evolution relate to the factors, not to the fact, of evolution, 347. Nature of the question: not metaphysical, not theological, but historical, 348. The historical method applied to the study of animal life, 349. The diversity of living forms, 349. Are species fixed in nature? 350. Wide variation among animals, 350. Evolutionary series: The shells of Slavonia and Steinheim, 351-353. Evolution of the horse, 354. The collection of fossil horses at the American Museum of Natural History, New York, 355. The genealogy of the horse traced for more than two million years, 354. Connecting forms: the archæopteryx and pterodactyls, 358. The embryological record and its connection with evolution, 358. Clues to the past history of animals, 358. Rudimentary organs, 361-363. Hereditary survivals in the human body, 363. Remains of the scaffolding for its building, 364. Antiquity of man, 364. Pre-human types, 365. Virtually three links: the Java man; the Neanderthal skull; the early neolithic man of Engis, 364-366. Evidences of man's evolution based on palæontology, embryology, and archæology, 366. Mental evolution, 366. Sweep of the doctrine of organic evolution, 366-367. CHAPTER XVII Theories of Evolution--Lamarck. Darwin, 368