Index. 
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 distribution 
of, 204-248 ; extinct and living 
allied on same areas, 213; life 
of, preserved by natural selec- 
tion, 264-270; not room for 
more than one rational, 344; 
characters of, 274-276, 286- 
295, 374-376 ; inter-sterility of 
allied, 374-376 ; mutual minis- 
tration of alleged, 445, 446. 
Specific characters, see Characters. 
Speculation, method of, 3-9. 
Spencer, Herbert, on reproduction 
as discontinuous growth, 105, 
106; on use-inheritance, 253- 
256; his failure to conceive the 
idea of natural selection, 257. 
Spermatozoa, 123, 126-128. 
Spiders, in primary formations, 
163; courtship of, 388, 389. 
Spanges, 122, 139, 140. 
Spontaneous, Darwin’s use of the 
term, 340. 
Spores, 115. 
Squirrels, flying. 355. 
Sterility, see Infertility. 
St. Helena, 231-234, 236-237. 
St. Hilaire, 4. : 
Stick-insect, 322. 
Stoat, 318. 
Strombus accipitrinus, 2¢7 
Strombus Leidty, 201. 
Struggle for existence, 259-270. 
Subjective, methods, 6. 
Survival of the fittest, 335. See 
also Natural selection. 
Swim-bladder of fish, 154, 354. 
Symbiosis, 269. 
Syme, David, on the theory of 
natural selection, 340, 341. 
T. 
Tail, types of, in fish and birds, 
169-173. 
Tasmanian wolf, dentition of, 39. 
459 
Teeth, of Tasmanian wolf, 39; 
molar, of man, compared with 
those of apes, 92-94; palzeon- 
tology of horses’, 189-191. 
Temperature, sense of, probable 
origin of that of sight, 353, 354. 
Tennyson, 266. 
Tibiee, flattening of, 95, 96. 
Tissue-cells, see Cell. 
Toes, 79, 80; see also Feet. 
Tomes, C.S., on molar teeth of 
man and apes, 94. 
Torpedo, 365, 367. 
Tortoise, embryology of, 152, 
154. 
Toxopneustes variegatus, and 7. 
lividus, 122. 
Transport of organisms, means of, 
207, 216-218. 
Tribal fitness, as distinguishcd 
from individual, 267-269. 
Trout, ovum of, 122. 
Turtle, eye of, 75. 
Tylor, Alfred, on colouration of 
animals, 448-450. 
Type, preserved by natural selec- 
tion, 264-269 ; improvement of, 
by natural selection, 269, 270; 
prophetic, 272, 351-362. 
Types, as simple and generalized, 
33- 
Unicellular organisms, 104. 
Oraster, 138. 
Utility, of specific characters, 274, 
2753 of incipient characters, 
351-363; of electric organs, 
355 373: 
Vi 
Variation, in relation to natural 
selection, 263, 335-349, 377- 
Verification, 6-9. ~ 
Veitebral column, embryology of 
145, 146; paleontology of, 
192, 193. 
Vertebrated animal, ideal primi- 
tive, 143, 144; embryology of, 
143-155. 
Vespa vulgaris, 331. 
Vestigial organs, 65-97. 
Volucella inans, and V. bomby- 
Jans, 329. 
