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, 204-24S ; 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, 4,45, 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 nntural 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. 



Stromhus accipitrinus, 2C' 



Strombus LeUy. 201. 



Struggle for existence, 259-270. 



Subjective, methods, 6. 



SuiTival 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, 



Fail, 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', 1 89- 1 9 1. 



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 vanegatus, and T. 

 lividtis, 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- 



U. 



Unicellular organisms, 104. 



U> aster, 138. 



Utility, of specific characters, 274, 

 275 ; of incipient characters, 

 351-363 ; of electric organs, 



365-373- 



V. 



Variation, in relation to natural 

 selection, 263, 335-340, 377. 



Verification, 6-9. 



Vertebral column, embryology of 

 145, 1 46 ; palaeontology of, 

 192, 193. 



Vertebrated animal, ideal primi- 

 tive, 143, 144; embryology of, 



143-15.V 

 Vespa vulgaris, 331. 

 Vestigial organs, 65-97. 

 Volucella inans, and V. bomhy- 



tans, 329. 



