6.

Rattle-snake, tail of, 289.

Recognition marks, 271-273.

Religion, in relation to Darwinism, 401-418.

Reproduction, different methods of, 106-117;
essence of sexual, 110;
foreshadowing of sexual in unicellular organisms, 115-117.

Reptiles, wing of flying, 56;
rudimentary limbs of, 67;
nictitating membrane of, 75;
branchial arches of, 150;
embryology of, 152;
palaeontology of, 163, 165, 178-180;
brain of, 194-197;
distribution of, 224-240.

_Rhinoceros_, foot of, 186.

Robinson, Dr L., on grasping power of an infant's hands, 80-82.

Rudimentary organs, 65-97.

Ruminants, palaeontology of, 167, 168.

S.

Sacrum of man, compared with that of apes, 82-84.

_Sagitta_, 138.

Salamander, young of terrestrial, living in water, 102;
embryology of, 152.

Sandwich Islands, 234-237.

Science, method of, 1-9.

Sclater, W. L., on a case of mimicry, 331, 332.

Scorpion in Silurian formation, 163.

Sea, lamprey, 148;
destructive agency of the, 423, 424.

Seal, 51, 52, 75.

Seasonal changes of colour, 317-319.

Selection, value, 275;
by physical processes, 282, 283, 335. _See also_ Natural selection,
Artificial selection, Sexual selection, Physiological selection.

Sentiency, in relation to the theory of evolution, 417.

Sex, difference of, restricted to Metazoa and Metaphyta, 105.

Sexual reproduction, _see_ Reproduction.

Sexual selection, theory of, 277, 378-410;
statement and evidences of, 379-391;
criticisms of, 391-400;
includes law of battle with that of charming, 385, 386;
in relation to religious thought, 411-418;
Tylor's theory substituted for, by Wallace, 449, 450.

Shark, eye of, 75;
man-eating, 149;
and pilot-fish, 289.

Sheep, limb-bones of, 176, 177;
portraits of, 310.

Shells, of crabs, 62-64;
palaeontology of mollusks, 199-203;
land on oceanic islands, 224-240.

Silliman's Journal, on fauna of the Mammoth Cave, 70.

Skate, electric organ of, 364-373.

Skull, palaeontology of, 194-199;
of bull-dog compared with that of deer-hound, 307.

Slavonia, Tertiary deposits of, 18, 19.

Species, not eternal, but either created or evolved, 13;
named as such through absence of intermediate forms, 18-20;
groups of, in classification, 20,
and appearing suddenly in geological formations, 427-432, 437-440;
origin of, coincide in space and time with pre-existing and allied
species, 22;
geographical dis