Photograph of Élie Metchnikoff _Frontispiece_ _Figs._ _Page_ 1. _Catasetum saccatum_ 24 2. _Herminium monorchis_ 26 3. _Cerceris_ 28 4. _Listera ovata_ 32 5. _Pelopæus_ 34 6. Cæcum and vermiform appendage of man 44 7. Cæcum and vermiform appendage of chimpanzee 45 8. Fœtus of gibbon 46 9. Human fœtus 47 10. Fœtus of gorilla 50 11. Human fœtus 51 12. _Paramecium_ about to divide 230 13. Conjugation of _Paramecia_ 231 14. Section of a renal tubule invaded by Macrophags 241 15. Brain cells devoured by Macrophags 241 16. Hair becoming grey 243 17. _Chætogaster_ about to divide 265 18. Ephemerids 271 19. Swarms of _Palingenia virgo_ 273 20. Larva of an Ephemerid 276 THE NATURE OF MAN PART I DISHARMONIES IN THE NATURE OF MAN CHAPTER I INTRODUCTION SUMMARY OF OPINIONS ON THE NATURE OF MAN Importance of the study of the nature of man—The nature of man as the foundation of morality—Greek worship of human nature—Matriopathy of ancient philosophers—Rationalism of the eighteenth and nineteenth centuries—Degradation of human nature by religious doctrines—Influence of these conceptions on actual life and on art—Reaction of the Reformation against the degradation of human nature—Mutilation of the human body by primitive races Notwithstanding the real advance made by science, expressions of discontentment with it are familiar. Science, it is said, no doubt has ameliorated the material conditions of human life, but is powerless to solve those moral and philosophical questions that interest cultured people so deeply. In this region science has done no more than to destroy the foundations of religion. It has robbed mankind of the consolations of religion without being able to replace them with anything more exact or more enduring.