Weismann, on the other hand, can only suppose that this intensely specialized instinct had its origin in fortuitous variations in the psychology of the species. But, neglecting the consideration that, in order to become fixed as an instinct by natural selection, the particular variation required must have occurred in many different individuals, not only in the first, but also in the sequent generations, the chances against its occurring only once, or in but one single individual case, are many thousands if not millions to one. INDEX A. Acceleration and retardation, 16. Acquired characters, heredity of, 39, 103, 133. Adaptation, 7, 13, 55, 62, 67, 71, 159, 165; of species and of specific characters, 166. ALLEN, Mr., referred to, 209. _All-sufficiency of Natural Selection_, referred to, 65, 95. _Alone with the Hairy Ainu_, referred to, 26. American and European trees compared, 201. _American Journal of Science_, referred to, 273. _American Naturalist_, referred to, 35, 58. Ammonites, species of, 254. _Animal Intelligence_, referred to, 93. _Animal Life_, referred to, 101. _Animal Life and Intelligence_, referred to, 33, 36. _Apparent Paradox in Mental Evolution_, referred to, 90. Appendages of Normandy and Irish pigs, 188. Articulation and inheritance, 335. Artistic faculties of man, 27. B. BABINGTON, Prof., referred to, 252. BACHMAN, Dr., referred to, 186. BAILEY, Prof., referred to, 127. BAKER, Mr., referred to, 252. Balancing of brainless frog, 78. BALL, Mr. Platt, referred to, 3, 95; quoted, 50. BATESON, Mr. W., referred to, 36. BEDDARD, Mr. F., referred to, 174. BENTHAM, Mr., referred to, 252. Birds, diagnostic characters of, 176; of Australia, effect of climate on, 210; influence of food on, 218. Blastogenetic, 123, 242, 245, 250. Blending of adaptations, 67. _Brain_, referred to, 80. BROCA, Prof., referred to, 64, 67, 174, 318. BRONN, Prof., referred to, 174. BROOKS, Prof., referred to, 14. BROWN-SÉQUARD, referred to, 104, 122, 142; quoted, 104. BUCKLEY, Mr., referred to, 147. BUCKMAN, Prof. James, referred to, 125. BUCKMAN, Prof. S.S., referred to, 24. BUTLER, Mr. A. G., referred to, 254. BUTLER, Mr. Samuel, referred to, 87. Butterfly, seasonal changes of, 210; influence of food on, 217. C. Carnivora, instincts of, 89. CARRIÈRE, M. L. A., referred to, 123. Cave animals, colour-changes in, 211. _Cave Fauna of North America_, quoted, 211. Cessation of Selection, 99, 199, 212, 292. Characters, adaptive and specific, 159, 307; specific, due to Natural Selection, 171. _Charadriidae, Geographical Distribution of the Family_, quoted, 173. Chimpanzee, counting of, 31. Climate, influence of, on plants, 200; on animals, 209. Co-adaptation, 64. COCKERELL, Prof., referred to, 218. Colour, 269. Colour-changes in butterflies, 210. in cave animals, 211. _Colours of Animals_, referred to, 36. Congenital, as opposed to acquired characters, 134.