_Chelydra serpentina_, anterior limb of, 179-181. Chick, embryology of, 153. Chimpanzee, _see_ Apes. Chlorophyll, 408. _Chondracanthus cornutus_, 122. Cirripedes, 430. Classification, 23-49; of organic nature by Genesis and Leviticus, 23; artificial and natural, 24-26; empirical rules of, 33-40; Darwin on, 35, 36, 39,40; form of, a nexus or tree, 29-32; of organic forms like that of languages, 32; single characters in relation to, 37; aggregates of characters in relation to, 35-37; adaptive and non-adaptive characters in relation to, 34, 35, 38, 39; chains of affinities in relation to, 39-40; biological differs from astronomical, 43. Cockerell, on vegetable galls, 447, 448. Colours, of plants and animals in relation to the theory of natural selection, 317-332; in relation to the theory of sexual selection, 391, 392, 394-396, 408-410, 448-450. Colouring, _see_ Recognition marks, Protective, Seasonal, Warning, and Mimicry. Congenital characters, _see_ Characters. Conjugation, of Protozoa, 115-117. Continuity, principle of, in nature, 15-21. Contrivance, Darwin's use of the word, 281. Co-operation, mutual, of species alleged, 445-448. Co-operative instincts, due to natural selection, 267, 269. Cope, Professor, his table of geological formations, 163, 164; his table of palæontological development of feet, vertebral column, and brain, 197. Correlation of growth, 357-362. _Cossonidæ_, 233. Courtship, _see_ Sexual Selection. Crabs, 62-65, 139. Cuttle-fish, 317. Cuvier, on method in natural history, 3-4; on monkeys, 429. Cyst, _see_ Encystation. D. Darwin, Charles, his influence on ideas of method, 1-9; on classification, 35, 36, 39, 40; on vestigial characters in man, 77, 86, 87, 92; on imperfection of geological record, 165, and Appendix; on means of dispersal, 216, 218; on geographical distribution, 218, 219; on fauna of the Galapagos Archipelago, 227, 228; on natural selection, 252, 253, 255, 256, 286, 375, 376; his use of such words as 'accident,' 'fortuitous,' 'purpose,' 'contrivance,' &c., 281, 334-340; on sexual selection, 379-400. Darwin, Erasmus, his theory of evolution, 253. De Blainville, on the theory of descent, 258. De Candolle, on classification, 34. Deer, 98, 99, 167-169, 187, 191, 196, 198, 199. Degeneration, 269, 270, 342. Delamination, 139. _Diadema euryta_, 330. Diaster, 129-133. Dingo, _see_ Dog. _Dinornis_, 60, 61. _Diptera_ mimicking _Hymenoptera_, 329. Dog, dentition of, 39; Dingo, 304; domesticated varieties of, 305, 307; hairless, 307; skulls of, 307. Duck, logger-headed, 68. Dugong, eye of, 75. E. Eagle, eye of, 75. Ear, of whales, 65; vestigial features of human, 76, 86-89; of man and apes compared, 88. Eaton, Rev. A. E., on wingless insects, 70. _Echinodermata_, 125-127, 138, 155. Ectoderm, 137-142. Egg, _see_ Ovum. Eimer, 363. _Elaps fulvius_ imitated by non-venomous snakes, 330.