birds, instinctive or imitative, 220.

SPECIES, law of population of, 28;
abundance or rarity of, dependent on the adaptation to
conditions, 33;
definition of, 141, 161;
the range and constancy of, 143;
extreme variation in, 163, 164.

SPEED of animals, limits of, 292.

_Sphecia craboniforme_, 90.

_Sphecomorpha chalybea_, 96.

SPHEGIDAE, mimicked by flies, 97.

SPIDERS, which mimic ants, 98;
and flower buds, 99.

_Spilosoma menthastri_, 88.

STAINTON, Mr., on moths rejected by turkeys, 78, 88.

STALACHTIS, a genus of Erycinidae, the object of mimicry, 84.

STINGING insects generally conspicuously coloured, 72.

STREPTOCITTA, 196.

STURNIDAE, sexual colouring and nidification of, 244.

STURNOPASTOR, 239.

ST. HELENA, 10.

_Streptolabis hispoides_, 93.

STRUGGLE for existence, 28, 33.

SURVIVAL of the fittest, law of, stated, 33;
its action in determining colour, 67.

SWAINSON'S circular and quinarian theory, 45.

SYLVIADAE, sexual colouring and nidification of, 245.

SYNAPTA, 258.

_TACHORNIS phoenicobea_, 228.

_Tachyris hombronii_, 172;
_ithome_, 172;
_lycaste_, 172;
_lyncida_, 172;
_nephele_, 172;
_nero_, 172;
_zarinda_, 172.

TANAGRIDAE, sexual colouring and nidification of, 245.

TAPIR, 299.

TELEPHORI, similar colouring of two sexes, 114.

TEMPERATE and cold climates favourable to civilization, 318.

THECODONTIA, 299.

THERATES, mimicked by Heteromera, 95.

_Thyca descombesi_, 172;
_hyparete_, 172;
_rosenbergii_, 172;
_zebuda_, 172.

TIGER, adaptive colouring of, 52.

TIMES newspaper on Natural Selection, 296.

TOOLS, importance of, to man, 314.

TREE FROGS, probable mimicry by, 103.

TRICONDYLA, 97.

TRIMEN, Mr., on rank of the Papilionidae, 136.

TRISTRAM, Rev. H., on colours of desert animals, 50.

_Trochilium tipuliforme_, 90.

TROGONIDAE, sexual colouring and nidification of, 241.

TROPICAL birds often green, 52.

TROPICS, most favourable to production of perfect adaptation among
animals, 68;
not favourable to growth of civilization, 318.

TROPIDORHYNCHUS mimicked by orioles, 104.

TRUTHFULNESS of some savages, 353;
not to be explained on utilitarian hypothesis, 354.

TURDIDAE, sexual colouring and nidification of, 245.

TURNIX, 115, 251.

TYNDALL, Professor, on origin