Rational Systematics 243 Biological Systematics 246 *B.* THE THEORY OF DESCENT-- 1. GENERALITIES 250 The Covert Presumption of all Theories of Descent 253 The Small Value of Pure Phylogeny 255 History and Systematics 257 2. THE PRINCIPLES OF DARWINISM 260 Natural Selection 261 Fluctuating Variation the Alleged Cause of Organic Diversity 264 Darwinism Fails all along the Line 269 3. THE PRINCIPLES OF LAMARCKISM 271 Adaptation as the Starting-Point 272 The Active Storing of Contingent Variations as a Hypothetic Principle 273 Criticism of the “Inheritance of Acquired Characters” assumed by Lamarckism 275 Other Principles Wanted 281 Criticism of the Hypothesis of Storing and Handing Down Contingent Variations 282 4. THE REAL RESULTS AND THE UNSOLVED PROBLEMS OF TRANSFORMISM 290 5. THE LOGICAL VALUE OF THE ORGANIC FORM ACCORDING TO THE DIFFERENT TRANSFORMISTIC THEORIES 293 The Organic Form and Entelechy 294 *C.* THE LOGIC OF HISTORY 297 1. THE POSSIBLE ASPECTS OF HISTORY 299 2. PHYLOGENETIC POSSIBILITIES 304 3. THE HISTORY OF MANKIND 306 Cumulations in Human History 308 Human History not an “Evolution” 311 The Problem of the “Single” as such 315 *CONCLUSIONS ABOUT SYSTEMATICS AND HISTORY IN GENERAL* 322 THE PROGRAMME ON LORD GIFFORD’S CONCEPTION OF “SCIENCE” This is the first time that a biologist has occupied this place; the first time that a biologist is to try to carry out the intentions of the noble and high-minded man to whom this lectureship owes its foundation. On such an occasion it seems to be not undesirable to inquire what Lord Gifford’s own opinions about natural science may have been, what place in the whole scheme of human knowledge he may have attributed to those branches of it which have become almost the centre of men’s intellectual interest.