CHAPTER XVIII

Theories Continued--Weismann. De Vries, 392

Weismann's views have passed through various stages of remodeling, 392. The Evolution Theory published in 1904 is the best exposition of his views, 392. His theory the field for much controversy. Primarily a theory of heredity, 393. Weismann's theory summarized, 393. Continuity of the germ-plasm the central idea in Weismann's theory, 394. Complexity of the germ-plasm. Illustrations, 395. The origin of variations, 396. The union of two complex germ-plasms gives rise to variations, 396. His extension of the principle of natural selection--germinal selection, 397. The inheritance of acquired characters, 398. Weismann's analysis of the subject the best, 398. Illustrations, 399. The question still open to experimental observation, 399. Weismann's personality, 400. Quotation from his autobiography, 401. The mutation theory of De Vries, 402. An important contribution. His application of experiments commendable, 403. The mutation theory not a substitute for that of natural selection, 404. Tendency toward a reconciliation of apparently conflicting views, 404. Summary of the salient features of the theories of Lamarck, of Darwin, of Weismann, and De Vries, 405. Causes for bewilderment in the popular mind regarding the different forms of the evolution theory, 406.