Index. 



459 



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- 

 2 95 374-3/6 ; 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. 



Sponges, 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, 201. 



Strombus Leidy, 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. 



Teeth, of Tasmanian wolf, 39 ; 

 molar, of man, compared with 

 those of apes, 92-94 ; palaeon- 

 tology of horses', 189-191. 



Temperature, sense of, probable 

 origin of that of sight, 353, 354. 



Tennyson, 266. 



Tibiae, 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 T. 



lividus, 122. 

 Transport of organisms, means of, 



207, 216-218. 

 Tribal fitness, as distinguished 



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. 



Uraster, 138. 



Utility, of specific characters, 274, 

 275 ; of incipient characters, 

 35 J -363 ; of electric organs, 



Variation, in relation to natural 



selection, 263, 335-34> 377- 

 Verification, 6-9. 

 Vertebral column, embryology of, 



145, 146 ; palaeontology of, 



192, 193. 

 Vertebrated animal, ideal primi- 



tive, 143, 144; embryology of, 



143-155. . 

 Vespa vulgans, 331. 

 Vestigial organs, 65-97. 

 Volucella inans, and V. bomby- 



lans, 329. 



