Sea squirts 35 _Segestria senoculata_ 83 Selection, sexual 5 Self-coloured flowers 28 Sense organs of Butterflies 30 _Sertularidæ_ 63 Sexual colours 4 ---- selection 5 ---- dimorphism 70 Shell, Structure of 85 Shore Crab 4 Simple variation in Butterflies 77 _Siphonophora_ 63 Small pox 39 Snakes, patterns of 89 Sollas, Prof., on Sponges 58 Soles 88 _Sparassus smaragdulus_ 82 Species, origin of 1 _Sphæronectes_ 63 _Sphingidæ_ 45, 69 Spiders, structure and colour of 82 Spiracles of larvæ 22 _Spondylus_ 86 Sponges 57 _Spongida_ 57 _Spongocyclia_ 57 Spots and Stripes 39 _Stephanomia amphitridis_ 63 Struggle for existence 2 Sun-birds 90 _Sus vittatus_ 46, 94 Sutton, Mr. Bland, on Herpes 40 Swallow-tailed Butterflies 68 _Syncoryne pulchella_ 62 Systems of colouration 51 Teeth and Hair, correlation of 94 _Thomisus cinereus_ 82 ---- _floricolens_ 82 _Thomisus luctuosus_ 84 ---- _trux_ 82 Thrush, increase of 2 Tiger 17, 92 ---- Moths 69 _Tipula_ 33 Toucans 90, 92