Segmentation of skull, 172.

Segmentation of spine, 171.

Segments, similar, 160.

Self-existence, 252.

Semnopithecus, 139.

Sense, organ of, 51, 69, 74, 76.

Sensitiveness of generative system, 235.

Sepia, 77.

Serpents, poisonous, 50.

s.e.xual characters of apes, 49.

s.e.xual selection, 48.

Sharks, 83.

Sh.e.l.l-fish, beauty of, 54.

Sh.e.l.ls of oysters, 88, 98.

Shielded gra.s.shopper, 89.

Silurian strata, 140, 142.

Simultaneous modifications, 57.

Sirenia, 42 Sir John Lubbock, 198, 204.

Sir William Thomson, 136.

Sitaris, 46.

Six-shafted bird of Paradise, 90.

Skull bones, 153.

Skull segments, 172.

Sloth, windpipe of, 82.

Smithfield, wife-selling in, 198.

Snow, crystals of, 186.

Sole, 37.

Solenodon, 148.

Species, meaning of word, 2.

Spelerpes, 165.

Spencer, see Herbert Spencer.

Spider orchid, 55.

Spiders, flight of, 65.

Spine of Glyptodon, 110.

Spine, segmentation of, 172.

Squalidae, 38.

Squilla, 160.

Sterility of hybrids, 125.

Stings, 66.

Straining action of baleen, 41.

Struthious birds, 70, 151.

Sturgeon, 171.

Suarez, 18, 263.

Substantial forms, 186, 272.

Sufferings of beasts, 260.

Supernatural action, 252.

Supernatural action not to be looked for in nature, 15.

Supernumerary digits, 122, 181.

Syllis, 169, 211.

Symbolic conceptions, 251.

Symmetrical diseases, 182.

Syphilitic deposits, 183.

T.

Tadpole's beak, 83.

Tails of b.u.t.terflies, 85.

Tapir, 123, 134.

Tarsal bones, 159, 198.

Teeth of Cetacea, 83.

Teeth of Insectivora, 68.

Teeth of kangaroo and Macroscelides, 69.

Teeth of seals, 83.

Teeth of sharks, 83.

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Teleology and evolution compatible, 273.

Tendrils of climbing plants, 107.

Tenia echinococcus, 170.

Teratology, 173.

Tetragonopterina, 146.

Thomson, Sir William, 136.

Thoracic fishes, 39.

Thorax of crustaceans, 79.

Thylacine, 67.

Tierra del Fuego, 192.

Tiger, sabre-toothed, 110.

Time required for evolution, 128.

Tope, 172.

Trabeculae cranii, 172.

Transitional forms, 128.

Trans.m.u.tationism, 242.

Trevelyan, Sir J. Peac.o.c.k, 100.

Trilobites, 135, 141, 171.

Tunicaries, 81.

Turbot, 37.

Turkey, effects of climate on, 100.

Turkish dog, 45.

Two-gilled cephalopods, 76.

Type, conformity to, 241.

U.

Umbilical vesicle, 82.

Ungulata, 25, 109.

Ungulata eocene, 110.

Units, physiological, 168, 218.

Unknowable, the, 245.

Upper Silurian strata, 140, 142.

Urotrichus, 68.

V.

Variability, different degrees of, 119.