Structure, degrees of utility of, 201.
Struggle for existence, 60.
Succession, geological, 312.
Succession of types in same areas, 338.
Swallow, one species supplanting another, 76.
Swim-bladder, 190.
System, natural, 413.
T.
Tail of giraffe, 195.
of aquatic animals, 196.
, rudimentary, 454.
Tarsi deficient, 135.
Tausch on umbelliferous flowers, 146.
Teeth and hair correlated, 144.
, embryonic, traces of, in birds, 451.
, rudimentary, in embryonic calf, 450, 480.
Tegetmeier, Mr., on cells of bees, 228, 233.
Temminck on distribution aiding classification, 419.
Thouin on grafts, 262.
Thrush, aquatic species of, 185.
, mocking, of the Galapagos, 402.
, young of, spotted, 439.
, nest of, 243.
Thuret, M., on crossed fuci, 258.
Thwaites, Mr., on acclimatisation, 140.
Tierra del Fuego, dogs of, 215.
, plants of, 374, 378.
Timber-drift, 360.
Time, lapse of, 282.
Titmouse, 183.
Toads on islands, 393.
Tobacco, crossed varieties of, 271.
Tomes, Mr., on the distribution of bats, 394.
Transitions in varieties rare, 172.
Trees on islands belong to peculiar orders, 392.
with separatd sexes, 99.
Trifolium pratense, 73, 94.
incarnatum, 94.
Trigonia, 321.
Trilobites, 306.
, sudden extinction of, 321.
Troglodytes, 243.
Tucutucu, blind, 137.
Tumbler pigeons, habits of, hereditary, 214.
, young of, 446.
Turkey-cock, brush of hair on breast, 90.
Turkey, naked skin on head, 197.
, young, wild, 216.
Turnip and cabbage, analogous variations of, 159.
Type, unity of, 206.
Types, succession of, in same areas, 338.
U.
Udders enlarged by use, 11.
, rudimentary, 451.
Ulex, young leaves of, 439.
Umbelliferæ, outer and inner florets of, 144.
Unity of type, 206.
Use, effects of, under domestication, 11.
, effects of, in a state of nature, 134.
Utility, how far important in the construction of each part, 199.
V.
Valenciennes on fresh-water fish, 384.
Variability of mongrels and hybrids, 274.
Variation under domestication, 7.
caused by reproductive system being affected by conditions of life, 8.
under nature, 44.
, laws of, 131.
Variations appear at corresponding ages, 14, 86.
, analogous in distinct species, 159.
Varieties, natural, 44.
, struggle between, 75.
, domestic, extinction of, 111.
, transitional, rarity of, 172.
, when crossed, fertile, 267.
, when crossed, sterile, 269.
, classification of, 423.
Verbascum, sterility of, 251.
, varieties of, crossed, 270.
Verneuil, M. de, on the succession of species, 325.
