The hereditary substance and the bearers of heredity, 305. The nature of inheritance, 305. Darwin's theory of pangenesis, 306. The theory of pangens replaced by that of germinal continuity, 307. Exposition of the theory of germinal continuity, 308. The law of cell-succession, 309. _Omnis cellula e cellula_, 309. The continuity of hereditary substance, 309. Early writers, 310. Weismann, 310. Germ-cells and body cells, 310. The hereditary substance is the germ-plasm, 311. It embodies all the past history of protoplasm, 311. The more precise investigation of the material basis of inheritance, 311. The nucleus of cells, 311. The chromosomes, 312. The fertilized ovum, the starting-point of new organisms, 313. Behavior of the nucleus during division, 313. The mixture of parental qualities in the chromosomes, 313. Prelocalized areas in the protoplasm of the egg, 314. The inheritance of acquired characteristics, 314. The application of statistical methods and experiments to the study of heredity, 314. Mendel's important discovery of alternative inheritance, 316. Francis Galton, 317. Carl Pearson, 318. Experiments on inheritance, 318. CHAPTER XV The Science of Fossil Life, 320 Extinct forms of life, 320. Strange views regarding fossils, 320. Freaks of nature, 321. Mystical explanations, 321. Large bones supposed to be those of giants, 322. Determination of the nature of fossils by Steno, 322. Fossil deposits ascribed to the Flood, 323. Mosaic deluge regarded as of universal extent, 324. The comparison of fossil and living animals of great importance, 325. Cuvier the founder of vertebrate palæontology, 325. Lamarck founds invertebrate palæontology, 326. Lamarck's conception of the meaning of fossils more scientific than Cuvier's, 327. The arrangement of fossils in strata, 328. William Smith, 328. Summary of the growth of the science of fossil life, 329. Fossil remains as an index to the past history of the earth, 330. Epoch-making work of Charles Lyell, 330. Effect of the doctrine of organic evolution on palæontology, 332. Richard Owen's studies on fossil animals, 332. Agassiz and the parallelism between fossil forms of life and stages in the development of animals, 334. Huxley's geological work, 335. Leidy, 337. Cope, 337. Marsh, 338. Carl Zittel's writings and influence, 338. Henry F. Osborn, 339. Method of collecting fossils, 340. Fossil remains of man, 340. Discoveries in the Fayûm district of Africa, 341. PART II The Doctrine of Organic Evolution CHAPTER XVI What Evolution Is: The Evidence upon which it Rests, etc., 345