XXV. ABOUT CHOLERA 237 XXVI. SEA-BREEZES, MOUNTAIN AIR, AND OZONE 251 XXVII. OXYGEN GAS FOR ATHLETES AND OTHERS 258 XXVIII. SPARROWS, TROUT, AND SELECTIVE BREEDING 266 XXIX. THE FEEBLE-MINDED 271 XXX. DEATH-RATES 283 XXXI. GOSSAMER 287 XXXII. THE JUMPING BEAN 296 XXXIII. PROTECTIVE COLOURING IN ANIMALS 304 XXXIV. HOP-BLIGHT 314 XXXV. GREEN-FLIES, PLANT-LICE, AND PARTHENOGENESIS 322 XXXVI. THE DEADLY PHYLLOXERA 334 XXXVII. CLOTHES MOTHS 339 XXXVIII. STONE AND WOOD BORERS 346 XXXIX. CHRISTMAS FARE 356 XL. THE ORIGIN OF OPIUM 363 XLI. THE MOST ANCIENT MEN 371 XLII. THE CAVE-MEN’S SKULLS 391 XLIII. MORE ABOUT THE NEANDER MEN 402 INDEX 413 LIST OF ILLUSTRATIONS DIAGRAMS IN THE TEXT FIG. PAGE 1. THE LITTLE GREEN TREE-FROG OR “RAINETTE” OF THE RIVIERA (_HYLA ARBOREA_) 51 2. THE COMMON JELLY-FISH (_AURELIA AURITA_) 59 3. THE FRESH-WATER JELLY-FISH (_LIMNOCODIUM_) 60 4. FOUR JELLY-FISH-PRODUCING POLYPS ADHERING TO A ROOT-FIBRE OF A WATER-PLANT 61 5. THE AFRICAN FRESH-WATER JELLY-FISH (_LIMNOCNIDA_) 62 6. YOUNG STAGES OF THE COMMON EEL 72 7. DRAWING OF AN IVORY CARVING OF A FEMALE HEAD 80 8. DRAWING OF A FULLY ROUNDED CARVING IN REINDEER’S ANTLER OF THE HEAD OF A NEIGHING HORSE 80 9. DRAWING OF A FLAT CARVING IN SHOULDER-BONE OF A HORSE’S HEAD, SHOWING TWISTED ROPE-BRIDLE AND TRAPPINGS 81 10. FORE-FOOT OF THE HORSE-ANCESTOR, HIPPARION 84 11. SKULLS OF HORSES AND OF DEER 86 12. FORE AND HIND LEGS OF HORSE AND ASS 88 13. DIAGRAM OF THE UNDER SURFACE OF THE FOOT IN THE DOG, TAPIR, AND HORSE 89