| Fig. 1. | — Frontal view of the Cranial Dome of Pithecanthropus | [16] |
| Fig. 2. | — Frontal view of the same Greek skull as that shown in the frontispiece | [16] |
| Fig. 3. | — Eoliths, of ‘borer’ shape, from Ightham, Kent | [18] |
| Fig. 4. | — Eoliths of trinacrial shape, from Ightham, Kent | [20] |
| Fig. 5. | — Brain casts of four large Mammals | [23] |
| Fig. 6. | — Spironema pallidum, the microbe of Syphilis discovered by Fritz Schaudinn | [37] |
| Fig. 7. | — The Canals in Mars | [43] |
| Fig. 8. | — The Canals in Mars | [44] |
| Fig. 9. | — Becquerel’s shadow-print obtained by rays from Uranium Salt | [73] |
| Fig. 10. | — Diagrams of the visible lines of the Spectrum given by incandescent Helium and Radium | [76] |
| Fig. 11. | — The transformation of Radium Emanation into Helium (spectra) | [83] |
| Fig. 12. | — Dry-plate photograph of a Nebula and surrounding stars | [90] |
| Fig. 13. | — The Freshwater Jelly fish, Limnocodium | [97] |
| Fig. 14. | — Polyp of Limnocodium | [97] |
| Fig. 15. | — Sense-organ of Limnocodium | [97] |
| Fig. 16. | — The Freshwater Jelly-fish of Lake Tanganyika | [98] |
| Fig. 17. | — Sir Harry Johnston’s specimen of the Okapi | [99] |
| Fig. 18. | — Bandoliers cut from the striped skin of the Okapi | [99] |
| Fig. 19. | — Skull of the horned male of the Okapi | [100] |
| Fig. 20. | — The metamorphosis of the young of the common Eel | [101] |
| Fig. 21. | — A unicellular parasite of the common Octopus, producing spermatozoa | [102] |
| Fig. 22. | — The Coccidium, a microscopic parasite of the Rabbit, producing spermatozoa | [102] |
| Fig. 23. | — Spermatozoa of a unicellular parasite inhabiting a Centipede | [103] |
| Fig. 24. | — The motile fertilizing elements (antherozoids or spermatozoa) of a peculiar cone-bearing tree, the Cycas revoluta | [104] |
| Fig. 25. | — The gigantic extinct Reptile, Triceratops | [106] |
| Fig. 26. | — A large carnivorous Reptile from the Triassic rocks of North Russia | [107] |
| Fig. 27. | — The curious fish Drepanaspis, from the Old Red Sandstone of Germany | [107] |
| Fig. 28. | — The oldest Fossil Fish known | [108] |
| Fig. 29. | — The skull and lower jaw of the ancestral Elephant, Palæomastodon, from Egypt | [109] |
| Fig. 30. | — The latest discovered skull of Palæomastodon | [110] |
| Fig. 31. | — Skulls of Meritherium, an Elephant ancestor, from the Upper Eocene of Egypt | [111] |
| Fig. 32. | — The nodules on the roots of bean-plants and the nitrogen-fixing microbe, Bacillus radicola, which produces them | [114] |
| Fig. 33. | — The continuity of the protoplasm of vegetable cells | [116] |
| Fig. 34. | — Diagram of the structures present in a typical organic ‘cell’ | [117] |
| Fig. 35. | — The Number of the Chromosomes | [119] |
| Fig. 36. | — The Number of the Chromosomes | [120] |
| Figs. 37 to 42. — Phagocytes engulphing disease germs— drawn by Metschnikoff | [136-7] |
| Fig. 43. | — A Phagocyte containing three Spirilla, the germs of relapsing fever, which it has engulphed | [137] |
| Fig. 44. | — The life-history of the Malaria Parasite | [142] |
| Fig. 45. | — The first blood-cell parasite described, the Lankesterella of Frog’s blood | [144] |
| Fig. 46. | — Various kinds of Trypanosomes | [145] |
| Fig. 47. | — The Laboratory of the Marine Biological Association on the Citadel Hill, Plymouth | [155] |
| Fig. 48. | — The Tsetze fly, Glossina morsitans | [172] |
| Fig. 49. | — The Trypanosome of Frog’s blood | [173] |
| Fig. 50. | — The Trypanosome which causes the Sleeping Sickness | [176] |
| Fig. 51. | — The Trypanosome of the disease called “Dourine” | [177] |
| Figs. 52 to 56. — Stages in the growth and multiplication of a Trypanosome which lives for part of its life in the blood of the little owl, Athene noctua, and for the other part in the gut of the common Gnat (Culex) | [180-3] |