| FIG. | PAGE | |
| 1. | Diagram of a Cell. (Drawn by Mr. E. P. Copeland from a sketch by the Author.) | 5 |
| 2. | Stylonychia. (Drawn by Mr. E. P. Copeland.) | 9 |
| 3. | Amœba. (Drawn by Mr. E. P. Copeland.) | 11 |
| 4. | Rotalia. (Drawn by Dr. A. L. Lawrence.) | 12 |
| 5. | Difflugia. (Drawn by Dr. A. L. Lawrence.) | 17 |
| 6. | Noctiluca. (Drawn by Dr. A. L. Lawrence.) | 18 |
| 7. | Gromia. (Drawn by Dr. A. L. Lawrence.) | 21 |
| 8. | Diagram Illustrating Mitosis. (Drawn by Mr. E. P. Copeland from a sketch by the Author.) | 26 |
| 9. | Diagram Illustrating the Maturation and Fertilization of the Ovum. (Drawn by Mr. E. P. Copeland from a sketch by the Author.) | 30 |
| 10. | Diagram Illustrating Segmentation and Gastrulation. (Drawn by Mr. E. P. Copeland from a sketch by the Author.) | 34 |
| 11. | Archæan North America. (From a drawing in Shaler’s “First Book in Geology.”) | 84 |
| 12. | Cretaceous North America. (From a drawing in Shaler’s “First Book in Geology.”) | 86 |
| 13. | Tertiary North America. (From a drawing in Shaler’s “First Book in Geology.”) | 89 |
| 14. | Genesis of Horse’s Feet. (Drawn by Mr. E. P. Copeland.) | 112 |
| 15. | Bipes, Cheirotes, and Snake. (From a drawing in Shaler’s “First Book in Geology.”) | 114 |
| 16. | Domesticated Pig and Wild Boar. (From Romanes’ “Darwin and After Darwin.”) | 121 |
| 17. | Tadpoles and Frog. (Drawn by Dr. A. L. Lawrence.) | 175 |
| 18. | Diagram of Development. (Drawn by Mr. B. H. Esterly from a sketch by the Author.) | 183 |
| 19. | Brain of Fish. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 198 |
| 20. | Brain of Reptile. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 199 |
| 21. | Brain of a Marsupial. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 200 |
| 22. | Brain of a Lemur. (Modified by Mr. B. H. Esterly from Flower.) | 201 |
| 23. | Ideal Sections of Brains. (Modified from Le Conte. Drawn by Dr. A. L. Lawrence from a sketch by the Author.) | 202 |
| 24. | Brain of Human Fœtus—Fish Phase. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 204 |
| 25. | Brain of Human Fœtus—Reptile Phase. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 204 |
| 26. | Brain of Human Fœtus—Marsupial Phase. Side View. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 204 |
| 27. | Brain of Human Fœtus—Marsupial Phase. Dorsal View. (Drawn by Mr. B. H. Esterly from specimens of the Author.) | 205 |
| COLORED PLATES | ||
| PLATE | FACING PAGE | |
| I. | Wild Rock Pigeon and Pouter. (Drawn by Mr. J. L. Ridgway from specimens in the Smithsonian Institution.) | Frontispiece |
| II. | Butterflies. (Drawn by Miss L. Sullivan from specimens in the United States Bureau of Entomology.) | 138 |
| III. | Caterpillar of Geometer Moth. (Drawn by Miss L. Sullivan from specimens in the United States Bureau of Entomology.) | 142 |
| V. | Spider on Flower. (Drawn by Miss L. Sullivan from a plate in McCook’s “American Spiders.”) | 144 |
| VI. | Elaps and Erythrolamprus. (Modified by Mr. J. L. Ridgway from a figure in Romanes’ “Darwin and After Darwin.”) | 146 |
| VII. | Salamandra maculosa. (Drawn by Mr. J. L. Ridgway from specimens in the United States National Museum.) | 148 |
| VIII. | Paradise Birds. (Drawn by Mr. J. L. Ridgway from specimens in the Smithsonian Institution.) | 152 |
| IX. | Primrose Flowers. (Drawn by Miss L. Sullivan from specimens.) | 162 |
| X. | Bee Fertilizing Flower. (Drawn by Miss L. Sullivan from specimens in the United States Bureau of Entomology.) | 164 |
| PLATES ENGRAVED IN BLACK AND WHITE | ||
| IV. | Leaf-hoppers. (Drawn by Miss L. Sullivan from drawings collected by Dr. L. O. Howard.) | 140 |
| XI. | Babies’ Grasping Power. (From a Photograph taken by Dr. Louis Robinson.) | 192 |
| XII. | Brain of Man. (From Carus’ “The Soul of Man.”) | 202 |