_Scymnus_, an apterous species of, in Porto Santo, 82. Sea, inconstancy of insects in the vicinity of the, 57. Sicily, the fauna of, has much in common with that of Madeira, 139. _Silpha atrata_, Linn., presents a distinct state in Ireland, 33. _Silybum Marianum_, Grtn., its stalks the food of a _Ptinus_, 76. Similitudes, Lord Bacon on the importance of, 13. _Sitonia gressoria_, Illig., perhaps a form of the _S. grisea_, 33. _Sitophilus granarius_, Linn., unaffected by climate, 31. _Sitophilus oryzae_, Linn., unaffected by climate, 31. Sloths, their peculiarity to S. America, 143. Species, definition of the term, 4; familiar explanation concerning the nature of, 161, 162; limitation of, how to be attempted, 192; limits of, real, though often difficult to trace out, 193; in a certain sense both unstable and permanent, 194. Specific centres of creation, 5. _Sphinx Convolvuli_, Linn., its introduction into Madeira probably recent, 74. Spinola, on one of the _Reduviadae_, 101; on _Oncocephalus griseus_, 101. Stapelias, their concentration in Southern Africa, 142. States, large and small ones indicated in some insects, 105. Stature of insects, smaller in islands than on continents, 70. _Stenolophus Skrimshiranus_, Steph., perhaps a state of _S. Teutonus_, 63. _Stenus Heeri_, Woll., two distinct states of, indicated, 106. Structural characters, seldom variable in the Insecta, 95. Subsidences, the effect of, on insect life, 114. Swallow-Tail Butterfly, unaffected by climate, 31. _Syncalypta_, apterous in Madeira, 82. _Tachyporus nitidicollis_, Steph., perhaps a state of _T. obtusus_, 33. _Tarphii_, their economy in the Madeira Group, 121. _Tarphius_, its maximum attained in Madeira proper, 121; common to Madeira and Sicily, 139. _---- gibbulus_, Germ., the Sicilian exponent of the genus, 123. _---- Lowei_, Woll., of a more adaptive nature than its allies, 122. _Tarus_, always apterous in Madeira, 82. _---- lineatus_, Schoenh., assumes a distinct state in Madeira, 65. _Telephorus testaceus_, Linn., its variability in Lundy Island, 59. Thompson, Mr., on the reptiles of Ireland, England, and Belgium, 136. _Thorictus_, common to Madeira and Sicily, 139. Tierra del Fuego, insects of, 47; has many characters in common with Madeira, 48-51. Time, an important item in the question of modifications, 77. Toucans, their peculiarity to S. America and the W. Indies, 142. Transmutation-theory, unsoundness of the, 186-189; how it took its rise, 190. _Trechus_, always apterous in Madeira, 82. _---- alticola_, Woll., perhaps a state of _T. custos_, 39. _---- lapidosus_, Daws., pallid hue of, 64. Tree-Porcupines, their peculiarity to S. America, 143. _Tribolium ferrugineum_, Fabr., unaffected by climate, 31. _Trogosita mauritanica_, Linn., unaffected by climate, 31.