--- successively appearing, 312.
---- changing simultaneously throughout the world, 322.
Spencer, Lord, on increase in size of cattle, 35.
Sphex, parasitic, 218.
Spiders, development of, 442.
Spitz-dog crossed with fox, 268.
Sports in plants, 9.
Sprengel, C. C, on crossing, 98.
----, on ray-florets, 145.
Squirrels, gradations in structure, 180.
Staffordshire, heath, changes in, 71.
Stag-beetles, fighting, 88.
Sterility from changed conditions of life, 9.
---- of hybrids, 246.
---- ----, laws of, 255.
---- ----, causes of, 263.
---- from unfavourable conditions, 265.
---- of certain varieties, 269.
St. Helena, productions of, 390.
St. Hilaire, Aug., on classification, 418.
St. John, Mr., on habits of cats, 91.
Sting of bee, 202.
Stocks, aboriginal, of domestic animals, 18.
Strata, thickness of, in Britain, 284.
Stripes on horses, 163.
{501}
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, 450.
----, 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, 184.
Toads on islands, 393.
Tobacco, crossed varieties of, 271.
Tomes, Mr., on the distribution of bats, 395.
Transitions in varieties rare, 172.
Trees on islands belong to peculiar orders, 392.
---- with separated sexes, 99.
Trifolium pratense, 73, 94.
---- incarnatum, 94.
Trigonia, 321.
Trilobites, 307.
----, 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