— remarkable ornaments of, 225 Lucas, Dr. F. A., on sea-lions, 86 Males, degenerate, 307 — first to acquire new features, 9 — lead in new departures, 190 — where superfluous, 307 Mallard, remarkable behaviour of, 149 Man, evolution of, 22 _et seq._ “Mate-hunger,” part played by, 147 — power, importance of, 5 Mating, preferential, 155 May-flies, dance of death of, 229, 232 — nuptial flight of, 232 — remarkable eyes of male, 231 May-flies, remarkable use of stomach in, 230 Mayer, Mr., experiments on moths, 205 Moina, claspers of, 262 Moose, peculiar habits of, 58 Morgan, Professor Lloyd, on emotions, 18 — on factors in selection, 19, 126 Moth, aquatic females in, 204 — Eyed-hawk, display of, 201 — Ghost, scent-bottle of, 200 — Kentish Glory, sexual differences in, 203 — Oak-eggar, remarkable sense of smell in, 202 — Vapourer, remarkable sense of smell in, 201 Moths, bright colours of, 188 — diurnal, 189 — males, sense of smell of, 199 — scent organs of, 200 Mouth, brilliant colour in birds, 142 Muller, Fritz, on fragrant butterflies, 200 Music in birds, 123 _et seq._ Narwhal, tusk of, 90 Newts, courtship of, 170 — remarkable pairing habits of, 170 Ocelli in birds, nature of, 98 Octopus, courtship of, 267 — remarkable mating habits of, 268 Ornament, controlling factors of, 168 Orthogenesis, nature of, 17 Osborne, Professor, on factors in evolution, 17 Ostrich, roar of, 112 Oysters, helpless condition of, 274 — and social reformers, 275 Painted Terrapin, remarkable courtship of, 168 Parthenogenesis in Crustacea, 304 — occurrence of, 276 — significance of, 308 — types of, 300 Peacock, display of, 95 Peckham, Mr., on courtship in spiders, 241 Pheasants, display of, 100 Pigment intensification, cause of, 150 Plovers, fatal conflicts among, 117 — dances of, 119 Plumage, evolution of, 143 Polyandry, human, 29 — in birds, 134 — interpretation of, 136 Polygamy, human, 27 — in birds, 115, 135 — in ungulates, 75 — interpretation of, 76, 115, 135, 136 Poulton, Professor E. B., on animal coloration, 186 — on courtship of spiders, 245 — on sexual selection in spiders, 245 Prairie-hen, air-sacs in display of, 109 Pugnacity in birds, 116 Rays, remarkable teeth of, 176 Reproduction, forms of, 10 Rhinoceros, horns of, 75 Ruff, amorous instincts of, 115 — display of, 113 — variability of, 114 Sabre-toothed tiger, huge canines of, 80 — jaw-flanges of, 80 Salmon, coloration of, 180 — courtship of, 179 Sandpiper, Pectoral, air-sacs in display of, 108 Scent glands, 67 Scorpions, courtship of, 242 Secondary Sexual Characters, meaning of, 13 Selection, forms of, 7 Selous, Mr. F. C., on habits of moose, 59 — on the mane of the lion, 78 Sex, beginnings of, 4 — birth of, 12 Sex-antagonism, 9