i. 403;

explanation of, i. 256, 260, 271.

SELECTION, sexual and natural, contrasted, i. 278.

SELF-COMMAND, habit of, inherited, i. 92; estimation of, i. 95.

SELF-CONSCIOUSNESS, i. 62.

SELF-PRESERVATION, instinct of, i. 89.

SELF-SACRIFICE, by savages, i. 88; estimation of, i. 95.

SEMILUNAR fold, i. 23.

_Semnopithecus_, i. 197; long hair on the heads of species of, i. 192; ii. 380.

_Semnopithecus chrysomelas_, sexual differences of colour in ii. 291.

_Semnopithecus comatus_, ornamental hair on the head of, ii. 307.

_Semnopithecus frontatus_, beard, &c., of, ii. 308.

_Semnopithecus nasica_, nose of, i. 192.

_Semnopithecus nemaeus_, colouring of, ii. 310.

_Semnopithecus rubicundus_, ornamental hair on the head of, ii. 306.

SENSES, inferiority of Europeans to savages in the, i. 118.

SENTINELS, i. 74, 82.

SERPENTS, instinctively dreaded by apes and monkeys, i. 37, 42.

_Serranus_, hermaphroditism in, i. 208.

SEX, inheritance limited by, i. 282.

SEXES, relative proportions of, in man, i. 300, ii. 320; probable relation of the, in primeval man, ii. 362.

SEXUAL characters, secondary, i. 253; relations of polygamy to, i. 266; transmitted through both sexes, i. 279; gradation of, in birds, ii. 135.

SEXUAL and natural selection, contrasted, i. 278.

SEXUAL characters, effects of the loss of, i. 284; limitation of, i. 284.

SEXUAL differences in man, i. 14.

SEXUAL selection, explanation of, i. 256, 260, 271; influence of, on the colouring of Lepidoptera, i. 403; action of, in mankind, ii. 368.

SEXUAL similarity, i. 277.

SHARKS, prehensile organs of male, ii. 1.

SHARPE, R. B., on _Tanysiptera sylvia_, ii. 165; on _Ceryle_, ii. 173; on the young male of _Dacelo Gaudichaudi_, ii. 188.

SHAW, Mr., on the pugnacity of the male salmon, ii. 3.

SHAW, J., on the decorations of birds, ii. 71.

SHEEP, danger-signals of, i. 74; sexual differences in the horns of, i. 283; horns of, i. 289, ii. 246, 259; domestic, sexual differences of, late developed, i. 293; numerical proportion of the sexes in, i. 304; mode of fighting of, ii. 249; arched foreheads of some, ii. 284.

SHEEP, Merino, loss of horns in females of, i. 284; horns of, i. 289.

SHELLS, difference in form of, in male and female Gasteropoda, i. 324; beautiful colours and shapes of, i. 326.

SHIELD-DRAKE, pairing with a common duck, ii. 114; New Zealand, sexes and young of, ii. 206.

SHOOTER, J., on the Kafirs, ii. 347; on the marriage-customs of the Kafirs, ii. 373.

SHREW-MICE, odour of, ii. 279.

SHRIKE, Drongo, ii. 179.

SHRIKES, characters of young, ii. 185.

SHUCKARD, W. E., on sexual differences in the wings of Hymenoptera, i. 435.

SHYNESS of adorned male birds, ii. 97.

_Siagonium_, proportions of the sexes in, i. 314; dimorphism in males of, i. 374.

SIAM, proportion of male and female births in, i. 303.

SIAMESE, general beardlessness of the, ii. 321; notions of beauty of the, ii. 345; hairy family of, ii. 378.

SIEBOLD, C. T. von, on the auditory apparatus of the stridulant orthoptera, i. 353.

SIGHT, inheritance of long and short, i. 118.

SIGNAL-CRIES of monkeys, i. 57.

SILK-MOTH, difference of size of the male and female cocoons of the, i. 346; pairing of the, i. 401; male, fertilising two or three females, i. 406; proportion of the sexes in, i. 309, 311; Ailanthus, Prof. Canestrini, on the destruction of its larvae by wasps, i. 311.

SIMIADAE, i. 195; their origin and divisions, i. 213.

SIMILARITY, sexual, i. 277.

SINGING of the Cicadae and Fulgoridae, i. 351; of tree-frogs, ii. 27; of birds, object of the, ii. 52.

SIRENIA, nakedness of, i. 148.

_Sirex juvencus_, i. 365.

SIRICIDAE, difference of the sexes in, i. 365.

SISKIN, ii. 85; pairing with a canary, ii. 115.

_Sitana_, throat-pouch of the males of, ii. 33, 36.

SIZE, relative, of the sexes of insects, i. 345.

SKIN, movement of the, i. 19; nakedness of, in man, i. 148; colour of the, i. 241.

SKIN and hair, correlation of colour of, i. 248.

SKULL, variation of, in man, i. 108; cubic contents of, no absolute test of intellect, i. 145; Neanderthal, capacity of the, i. 146; causes of modification of the, i. 147; difference of, in form and capacity, in different races of men,