| | PAGE |
| 1. | Can we dispense with the principle of natural selection? | 255 |
| 2. | Nägeli’s theory of transformation from internal causes | 256 |
| 3. | A definite course of development is possible without a self-changing idioplasm | 258 |
| 4. | Conclusive importance of ‘adaptations’ | 260 |
| 5. | The structure of whales as an example of adaptation | 261 |
| 6. | Transformation takes place by the smallest steps | 264 |
| 7. | The foundation of such minute changes depends upon individual variability | 266 |
| 8. | Difficulty in accounting for variability on the supposition of a continuity of the germ-plasm | 266 |
| 9. | Previous theories by which variability has been accounted for | 267 |
| 10. | Non-transmission of acquired characters | 267 |
| 11. | Nägeli’s and Alexis Jordan’s experiments | 269 |
| 12. | Germ-plasm is only altered with great difficulty | 271 |
| 13. | The source of individual variation lies in sexual reproduction | 272 |
| 14. | The process of natural selection does not operate when asexual reproduction takes place | 274 |
| 15. | Origin of variability in unicellular organisms | 278 |
| 16. | Sexual reproduction effects combination | 279 |
| 17. | E. van Beneden’s and V. Hensen’s theory of sexual reproduction as a process of rejuvenescence | 282 |
| 18. | Theoretical objections to such a view | 283 |
| 19. | Original significance of conjugation | 286 |
| 20. | Preservation of sexual reproduction by means of heredity | 287 |
| 21. | It is lost in parthenogenesis for reasons of utility | 289 |
| 22. | Parthenogenesis prevents further transformations | 290 |
| 23. | It excludes Panmixia and thus prevents disused organs from becoming rudimentary | 291 |
| 24. | Final considerations | 294 |