Religions, 288;
  Christian, Hebrew, Buddhistic, Tangaroan, 289, 290;
  Mohammedan, 290, 298;
  Dervish, Mahdist, 293;
  linguistic basis of, 293, 294;
  of savagery, 294, 300, 301;
  barbarism, civilization, 294;
  elements of, 295;
  forms of Christianity, 296;
  sects,
    Judaism, 297, 298;
    Brahmanism, Buddhism, 298, 299;
    Polytheism, Roman, 300.

Reptiles, variations about a central theme, 45;
  lizard, typical, 46; 157;
  embryos of, 171; 200.

Retention of better invention, 109.

Rhinoceros, 41.

Rivers,
  Mississippi, 86, 89;
  Hoang-ho, Ganges, Thames, 87;
  alterations made by, 87.

Rocks, crystalline or plutonic: 
  sedimentary, 85;
  eruptive, 88;
  new, 59;
  of Grand Canon, 90;
  testimony of, establishes evolution, 100.

Salamanders, 45, 46.

Salts, of sodium, chlorine, magnesium, potassium, 24.

Samoan Islands, 103.

Sandstone, 90.

Science, what is it? 5, 6;
  physiological, 14.

Sea anemones, 68.

Sea elephant, 38.

Seals, 38, 39, 40, 209.

Selection,
  natural, doctrine of, 116, 117, 118;
  struggle for existence, 124, 125;
  simply trial and error, 131, 136,
  artificial, 136, 137, 138;
  laws of, in mental phenomena, 203.

Sequence, physiological, in training animals, 209; 210.

Series,
  sedimentary, 84, 90, 92;
  crystalline or plutonic, 85;
  Azoic or Archaean, age of, 92.

Shale, 89.

Shark,
  common, most fundamental form, 46;
  embryo of, hammerhead;
  embryos of, 66.

Sheep, 157.

Simiidae, 160, 163.

Skate, embryos of, 66.

Snails, 45;
  shells of, 95;
  land snails, 103;
  Hawaiian and Polynesian, 104.

Society Islands, 103.

Solar system, origin of, 84.

Solomon Islands, 103.

Species, origin of human, 153.

Spencer, Herbert, 8.

Squirrels,
  evolved from terrestrial rodents, 14; 41;
  flying, true rodents, 41.

Starch, 24.

Stephenson, 10.

Strata, 88, 89;
  arranged according to ages, 89; 90;
  time of formation, 92.

Struggle for existence, 124;
  intra-specific, 125;
  three divisions of, 126-129; 139, 174, 175.

Substances, inorganic, 29.

Sugar, 23, 24.

Survival of the fittest, 129.

Systems,
  respiratory, excretory, circulatory, 17;
  organic, reproductive, 18;
  nervous, 256, 257;
  blood-vascular, respiratory and excretory, 257;
  ethical, 286;
  religious, 288.

Tadpole, 58, 59, 60;
  larvae, 64.

Tapeworm, a relative of simple worms, 50; 123.

Tapir, 41;
  Moeritherium, 97.