163 ‘Hist. of British Birds,’ vol. ii. p. 92.

164 ‘Zoologist,’ 1853-1854, p. 3946.

165 Waterton, ‘Essays on Nat. Hist.’ 2nd series, p. 42, 117. For the following statements, see on the wigeon, Loudon’s ‘Mag. of Nat. Hist.’ vol. ix. p. 616; L. Lloyd, ‘Scandinavian Adventures,’ vol. i. 1854, p. 452; Dixon, ‘Ornamental and Domestic Poultry,’ p. 137; Hewitt, in ‘Journal of Horticulture,’ Jan. 13, 1863, p. 40; Bechstein, ‘Stubenvögel,’ 1840, s. 230.

166 Audubon, ‘Ornitholog. Biography,’ vol. i. p. 191, 349; vol. ii. p. 42, 275; vol. iii. p. 2.

167 ‘Rare and Prize Poultry,’ 1854, p. 27.

168 ‘The Variation of Animals and Plants under Domestication,’ vol. ii. p. 103.

169 Boitard and Corbié, ‘Les Pigeons,’ 1824, p. 12. Prosper Lucas (‘Traité de l’Héréd. Nat.’ tom. ii. 1850, p. 296) has himself observed nearly similar facts with pigeons.

170 ‘Die Taubenzucht,’ 1824, s. 86.

171 ‘Ornithological Biography,’ vol. i. p. 13.

172 ‘Proc. Zool. Soc.’ 1835, p. 54. The japanned peacock is considered by Mr. Sclater as a distinct species, and has been named Pavo nigripennis.

173 Rudolphi, ‘Beyträge zur Anthropologie,’ 1812, s. 184.

174 ‘Die Darwin’sche Theorie, und ihre Stellung zu Moral und Religion,’ 1869, s. 59.

175 In regard to peafowl, see Sir R. Heron, ‘Proc. Zoolog. Soc.’ 1835, p. 54, and the Rev. E. S. Dixon, ‘Ornamental Poultry,’ 1848, p. 8. For the turkey, Audubon, ibid. p. 4. For the capercailzie, Lloyd, 'Game Birds of Sweden,’ 1867, p. 23.

176 Mr. Hewitt, quoted in ‘Tegetmeier’s Poultry Book,’ 1866, p. 165.

177 Quoted in Lloyd’s ‘Game Birds of Sweden,’ p. 345.

178 According to Dr. Blasius (‘Ibis,’ vol. ii. 1860, p. 297), there are 425 indubitable species of birds which breed in Europe, besides 60 forms, which are frequently regarded as distinct species. Of the latter, Blasius thinks that only ten are really doubtful, and that the other fifty ought to be united with their nearest allies; but this shews that there must be a considerable amount of variation with some of our European birds. It is also an unsettled point with naturalists, whether several North American birds ought to be ranked as specifically distinct from the corresponding European species.

179 ‘Origin of Species,’ fifth edit. 1869, p. 104. I had always perceived, that rare and strongly-marked deviations of structure, deserving to be called monstrosities, could seldom be preserved through natural selection, and that the preservation of even highly-beneficial variations would depend to a certain extent on chance. I had also fully appreciated the importance of mere individual differences, and this led me to insist so strongly on the importance of that unconscious form of selection by man, which follows from the preservation of the most valued individuals of each breed, without any intention on his part to modify the characters of the breed. But until I read an able article in the ‘North British Review’ (March, 1867, p. 289, et seq.), which has been of more use to me than any other Review, I did not see how great the chances were against the preservation of variations, whether slight or strongly pronounced, occurring only in single individuals.

180 ‘Introduct. to the Trochilidæ,’ p. 102.

181 Gould, ‘Handbook of Birds of Australia,’ vol. ii. p. 32 and 68.

182 Audubon, ‘Ornitholog. Biography,’ 1838, vol. iv. p. 389.

183 Jerdon, ‘Birds of India,’ vol. i. p. 108; and Mr. Blyth, in ‘Land and Water,’ 1868, p. 381.

184 Graba, ‘Tagebuch, Reise nach Färo,’ 1830, s. 51-54. Macgillivray, 'Hist. British Birds,’ vol. iii. p. 745. ‘Ibis,’ vol. v. 1863, p. 469.

185 Graba, ibid. s. 54. Macgillivray, ibid. vol. v. p. 327.

186 ‘Variation of Animals and Plants under Domestication,’ vol. ii. p. 92.

187 On these points see also ‘Variation of Animals and Plants under Domestication,’ vol. i. p. 253; vol. ii. p. 73, 75.

188 See, for instance, on the irides of a Podica and Gallicrex in ‘Ibis,’ vol. ii. 1860, p. 206; and vol. v. 1863, p. 426.

189 See also Jerdon, ‘Birds of India,’ vol. i. p. 243-245.

190 ‘Zoology of the Voyage of H.M.S. Beagle,’ 1841, p. 6.

191 Bechstein, ‘Naturgeschichte Deutschlands,’ B. iv. 1795, s. 31, on a sub-variety of the Monck pigeon.

192 This woodcut has been engraved from a beautiful drawing, most kindly made for me by Mr. Trimen; see also his description of the wonderful amount of variation in the coloration and shape of the wings of this butterfly, in his, ‘Rhopalocera Africæ Australis,’ p. 186. See also an interesting paper by the Rev. H. H. Higgins, on the origin of the ocelli in the Lepidoptera in the ‘Quarterly Journal of Science,’ July, 1868, p. 325.

193 Jerdon, ‘Birds of India,’ vol. iii. p. 517.

194 ‘Variation of Animals and Plants under Domestication,’ vol. i. p. 254.

195 When the Argus pheasant displays his wing-feathers like a great fan, those nearest to the body stand more upright than the outer ones, so that the shading of the ball-and-socket ocelli ought to be slightly different on the different feathers, in order to bring out their full effect, relatively to the incidence of the light. Mr. T. W. Wood, who has the experienced eye of an artist, asserts (‘Field,’ Newspaper, May 28, 1870, p. 457) that this is the case; but after carefully examining two mounted specimens (the proper feathers from one having been given to me by Mr. Gould for more accurate comparison) I cannot perceive that this acme of perfection in the shading has been attained; nor can others to whom I have shewn these feathers recognise the fact.

196 ‘The Reign of Law,’ 1867, p. 247.

197 ‘Introduction to the Trochilidæ,’ 1861, p. 110.

198 Fourth edition, 1866, p. 241.

199 ‘Westminster Review,’ July, 1867. ‘Journal of Travel,’ vol. i. 1868, p. 73.

200 Temminck says that the tail of the female Phasianus Sœmmerringii is only six inches long, ‘Planches coloriées,’ vol. v. 1838, p. 487 and 488: the measurements above given were made for me by Mr. Sclater. For the common pheasant, see Macgillivray, ‘Hist. Brit. Birds,’ vol. i. p. 118-121.

201 Dr. Chapuis, ‘Le Pigeon Voyageur Belge,’ 1865, p. 87.

202 Bechstein, ‘Naturgesch. Deutschlands,’ 1793, B. iii. s. 339.

203 Daines Barrington, however, thought it probable (‘Phil. Transact.’ 1773, p. 164) that few female birds sing, because the talent would have been dangerous to them during incubation. He adds, that a similar view may possibly account for the inferiority of the female to the male in plumage.

204 Mr. Ramsay, in ‘Proc. Zoolog. Soc.’ 1868, p. 50.

205 ‘Journal of Travel,’ edited by A. Murray, vol. i. 1868, p. 78.

206 ‘Journal of Travel,’ edited by A. Murray, vol. i. 1868, p. 281.

207 Audubon, ‘Ornithological Biography,’ vol. i. p. 233.

208 Jerdon, ‘Birds of India,’ vol. ii. p. 108. Gould’s ‘Handbook of the Birds of Australia,’ vol. i. p. 463.

209 For instance, the female Eupetomena macroura has the head and tail dark blue with reddish loins; the female Lampornis porphyrurus is blackish-green on the upper surface, with the lores and sides of the throat crimson; the female Eulampis jugularis has the top of the head and back green, but the loins and the tail are crimson. Many other instances of highly conspicuous females could be given. See Mr. Gould’s magnificent work on this family.

210 Mr. Salvin noticed in Guatemala (‘Ibis,’ 1864, p. 375) that humming-birds were much more unwilling to leave their nests during very hot weather, when the sun was shining brightly, than during cool, cloudy, or rainy weather.

211 I may specify, as instances of obscurely-coloured birds building concealed nests, the species belonging to eight Australian genera, described in Gould’s ‘Handbook of the Birds of Australia,’ vol. i. p. 340, 362, 365, 383, 387, 389, 391, 414.

212 Jerdon, ‘Birds of India,’ vol. i. p. 244.

213 On the nidification and colours of these latter species, see Gould’s 'Handbook,’ &c., vol. i. p. 504, 527.

214 I have consulted, on this subject, Macgillivray’s ‘British Birds,’ and though doubts may be entertained in some cases in regard to the degree of concealment of the nest, and of the degree of conspicuousness of the female, yet the following birds, which all lay their eggs in holes or in domed nests, can hardly be considered, according to the above standard, as conspicuous: Passer, 2 species; Sturnus, of which the female is considerably less brilliant than the male; Cinclus; Motacilla boarula (?); Erithacus (?); Fruticola, 2 sp.; Saxicola; Ruticilla, 2 sp.; Sylvia, 3 sp.; Parus, 3 sp.; Mecistura; Anorthura; Certhia; Sitta; Yunx; Muscicapa, 2 sp.; Hirundo, 3 sp.; and Cypselus. The females of the following 12 birds may be considered as conspicuous according to the same standard, viz., Pastor, Motacilla alba, Parus major and P. cæruleus, Upupa, Picus, 4 sp., Coracias, Alcedo, and Merops.

215 ‘Journal of Travel,’ edited by A. Murray, vol. i. p. 78.

216 See many statements in the ‘Ornithological Biography.’ See, also, some curious observations on the nests of Italian birds by Eugenio Bettoni, in the ‘Atti della Società Italiana,’ vol. xi. 1869, p. 487.

217 See his ‘Monograph of the Trogonidæ,’ first edition.

218 Namely Cyanalcyon. Gould’s ‘Handbook of the Birds of Australia,’ vol. i. p. 133; see, also, p. 130, 136.

219 Every gradation of difference between the sexes may be followed in the parrots of Australia. See Gould’s ‘Handbook,’ &c., vol. ii. p. 14-102.

220 Macgillivray’s ‘British Birds,’ vol. ii. p. 433. Jerdon, ‘Birds of India,’ vol. ii. p. 282.

221 All the following facts are taken from M. Malherbe’s magnificent 'Monographie des Picidées,’ 1861.

222 Audubon’s ‘Ornithological Biography,’ vol. ii. p. 75; see also the 'Ibis,’ vol. i. p. 268.

223 Gould’s ‘Handbook of the Birds of Australia,’ vol. ii. p. 109-149.

224 See remarks to this effect in my work on ‘Variation under Domestication,’ vol. ii. chap, xii.

225 The ‘Ibis,’ vol. vi. 1864, p. 122.

226 On Ardetta, Translation of Cuvier’s ‘Règne Animal,’ by Mr. Blyth, footnote, p. 159. On the Peregrine Falcon, Mr. Blyth, in Charlesworth’s 'Mag. of Nat. Hist.’ vol. i. 1837, p. 304. On Dicrurus, ‘Ibis,’ 1863, p. 44. On the Platalea, ‘Ibis,’ vol. vi. 1864, p. 366. On the Bombycilla, Audubon’s ‘Ornitholog. Biography,’ vol. i. p. 229. On the Palæornis, see, also, Jerdon, ‘Birds of India,’ vol. i. p. 263. On the wild turkey, Audubon, ibid. vol. i. p. 15: I hear from Judge Caton that in Illinois the female very rarely acquires a tuft.

227 Mr. Blyth has recorded (Translation of Cuvier’s ‘Règne Animal,’ p. 158) various instances with Lanius, Ruticilla, Linaria, and Anas. Audubon has also recorded a similar case (‘Ornith. Biog.’ vol. v. p. 519) with Tyranga æstiva.

228 See Gould’s ‘Birds of Great Britain.’

229 In regard to thrushes, shrikes, and woodpeckers, see Mr. Blyth, in Charlesworth’s ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 304; also footnote to his translation of Cuvier’s ‘Règne Animal,’ p. 159. I give the case of Loxia from Mr. Blyth’s information. On thrushes, see also Audubon, 'Ornith. Biography,’ vol. ii. p. 195. On Chrysococcyx and Chalcophaps, Blyth, as quoted in Jerdon’s ‘Birds of India,’ vol. iii. p. 485. On Sarkidiornis, Blyth, in ‘Ibis,’ 1867, p. 175.

230 See, for instance, Mr. Gould’s account (‘Handbook of the Birds of Australia,’ vol. i. p. 133) of Cyanalcyon (one of the Kingfishers) in which, however, the young male, though resembling the adult female, is less brilliantly coloured. In some species of Dacelo the males have blue tails, and the females brown ones; and Mr. R. B. Sharpe informs me that the tail of the young male of D. Gaudichaudi is at first brown. Mr. Gould has described (ibid. vol. ii. p. 14, 20, 37) the sexes and the young of certain Black Cockatoos and of the King Lory, with which the same rule prevails. Also Jerdon (‘Birds of India,’ vol. i. p. 260) on the Palæornis rosa, in which the young are more like the female than the male. See Audubon (‘Ornith. Biograph.’ vol. ii. p. 475) on the two sexes and the young of Columba passerina.

231 I owe this information to Mr. Gould who shewed me the specimens; see also his ‘Introduction to the Trochilidæ,’ 1861, p. 120.

232 Macgillivray, ‘Hist. Brit. Birds,’ vol. v. p. 207-214.

233 See his admirable paper in the ‘Journal of the Asiatic Soc. of Bengal,’ vol. xix. 1850, p. 223; see also Jerdon, ‘Birds of India,’ vol. i. introduction, p. xxix. In regard to Tanysiptera, Prof. Schlegel told Mr. Blyth that he could distinguish several distinct races, solely by comparing the adult males.

234 See also Mr. Swinhoe, in ‘Ibis,’ July, 1863, p. 131; and a previous paper, with an extract from a note by Mr. Blyth, in ‘Ibis,’ Jan. 1861, p. 52.

235 Wallace, ‘The Malay Archipelago,’ vol. ii. 1869, p. 394.

236 These species are described, with coloured figures, by M. F. Pollen, in ‘Ibis,’ 1866, p. 275.

237 ‘Variation of Animals, &c., under Domestication,’ vol. i. p. 251.

238 Macgillivray, ‘Hist. British Birds,’ vol. i. p. 172-174.

239 See, on this subject, chap. xxiii. in the ‘Variation of Animals and Plants under Domestication.’

240 Audubon, ‘Ornith. Biography,’ vol. i. p. 193. Macgillivray, ‘Hist. Brit. Birds,’ vol. iii. p. 85. See also the case before given of Indopicus carlotta.

241 ‘Westminster Review,’ July, 1867, and A. Murray, ‘Journal of Travel,’ 1868, p. 83.

242 For the Australian species, see Gould’s ‘Handbook,’ &c., vol. ii. p. 178, 180, 186, and 188. In the British Museum specimens of the Australian Plain-wanderer (Pedionomus torquatus) may be seen, shewing similar sexual differences.

243 Jerdon, ‘Birds of India,’ vol. iii. p. 596. Mr. Swinhoe, in ‘Ibis,’ 1865, p. 542; 1866, p. 131, 405.

244 Jerdon, ‘Birds of India,’ vol. iii. p. 677.

245 Gould’s ‘Handbook of the Birds of Australia,’ vol. ii. p. 275.

246 ‘The Indian Field,’ Sept. 1858, p. 3.

247 ‘Ibis,’ 1866, p. 298.

248 For these several statements, see Mr. Gould’s ‘Birds of Great Britain.’ Prof. Newton informs me that he has long been convinced, from his own observations and from those of others, that the males of the above-named species take either the whole or a large share of the duties of incubation, and that they “shew much greater devotion towards their young, when in danger, than do the females.” So it is, as he informs me, with Limosa lapponica and some few other Waders, in which the females are larger and have more strongly contrasted colours than the males.

249 The natives of Ceram (Wallace, ‘Malay Archipelago,’ vol. ii. p. 150) assert that the male and female sit alternately on the eggs; but this assertion, as Mr. Bartlett thinks, may be accounted for by the female visiting the nest to lay her eggs.

250 ‘The Student,’ April, 1870, p. 124.

251 See the excellent account of the habits of this bird under confinement, by Mr. A. W. Bennett, in ‘Land and Water,’ May, 1868, p. 233.

252 Mr. Sclater, on the incubation of the Struthiones, ‘Proc. Zoo. Soc.’ June 9, 1863.

253 For the Milvago, see ‘Zoology of the Voyage of the “Beagle,”’ Birds, 1841, p. 16. For the Climacteris and nightjar (Eurostopodus), see Gould’s ‘Handbook of the Birds of Australia,’ vol. i. p. 602 and 97. The New Zealand shieldrake (Tadorna variegata) offers a quite anomalous case: the head of the female is pure white, and her back is redder than that of the male; the head of the male is of a rich dark bronzed colour, and his back is clothed with finely pencilled slate-coloured feathers, so that he may altogether be considered as the more beautiful of the two. He is larger and more pugnacious than the female, and does not sit on the eggs. So that in all these respects this species comes under our first class of cases; but Mr. Sclater (‘Proc. Zool. Soc.’ 1866, p. 150) was much surprised to observe that the young of both sexes, when about three months old, resembled in their dark heads and necks the adult males, instead of the adult females; so that it would appear in this case that the females have been modified, whilst the males and the young have retained a former state of plumage.

254 Jerdon, ‘Birds of India,’ vol. iii. p. 598.

255 Jerdon, ‘Birds of India,’ vol. i. p. 222, 228. Gould’s ‘Handbook of the Birds of Australia,’ vol. i. 124, 130.

256 Gould, ibid. vol. ii. p. 37, 46, 56.

257 Audubon, ‘Ornith. Biography,’ vol. ii. p. 55.

258 ‘Variation of Animals and Plants under Domestication,’ vol. ii. p. 79.

259 Charlesworth, ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 305, 306.

260 ‘Bulletin de la Soc. Vaudoise des Sc. Nat.’ vol. x. 1869, p. 132. The young of the Polish swan, Cygnus immutabilis of Yarrell, are always white; but this species, as Mr. Sclater informs me, is believed to be nothing more than a variety of the Domestic Swan (Cygnus olor).

261 I am indebted to Mr. Blyth for information in regard to this genus. The sparrow of Palestine belongs to the sub-genus Petronia.

262 For instance, the males of Tanagra æstiva and Fringilla cyanea require three years, the male of Fringilla ciris four years, to complete their beautiful plumage. (See Audubon, ‘Ornith. Biography,’ vol. i. p. 233, 280, 378.) The Harlequin duck takes three years (ibid. vol. iii. p. 614). The male of the Gold pheasant, as I hear from Mr. J. Jenner Weir, can be distinguished from the female when about three months old, but he does not acquire his full splendour until the end of the September in the following year.

263 Thus the Ibis tantalus and Grus Americanus take four years, the Flamingo several years, and the Ardea Ludovicana two years, before they acquire their perfect plumage. See Audubon, ibid. vol. i. p. 221; vol. iii. p. 133, 139, 211.

264 Mr. Blyth, in Charlesworth’s ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 300. Mr. Bartlett has informed me in regard to gold pheasants.

265 I have noticed the following cases in Audubon’s ‘Ornith. Biography. The Redstart of America’ (Muscicapa ruticilla, vol. i. p. 203). The Ibis tantalus takes four years to come to full maturity, but sometimes breeds in the second year (vol. iii. p. 133). The Grus Americanus takes the same time, but breeds before acquiring its full plumage (vol. iii. p. 211). The adults of Ardea cærulea are blue and the young white; and white, mottled, and mature blue birds may all be seen breeding together (vol. iv. p. 58): but Mr. Blyth informs me that certain herons apparently are dimorphic, for white and coloured individuals of the same age may be observed. The Harlequin duck (Anas histrionica, Linn.) takes three years to acquire its full plumage, though many birds breed in the second year (vol. iii. p. 614). The White-headed Eagle (Falco leucocephalus, vol. iii. p. 210) is likewise known to breed in its immature state. Some species of Oriolus (according to Mr. Blyth and Mr. Swinhoe, in ‘Ibis,’ July, 1863, p. 68) likewise breed before they attain their full plumage.

266 See the last footnote.

267 Other animals, belonging to quite distinct classes, are either habitually or occasionally capable of breeding before they have fully acquired their adult characters. This is the case with the young males of the salmon. Several amphibians have been known to breed whilst retaining their larval structure. Fritz Müller has shewn (‘Facts and Arguments for Darwin,’ Eng. trans. 1869, p. 79) that the males of several amphipod crustaceans become sexually mature whilst young; and I infer that this is a case of premature breeding, because they have not as yet acquired their fully-developed claspers. All such facts are highly interesting, as bearing on one means by which species may undergo great modifications of character, in accordance with Mr. Cope’s views, expressed under the terms of the “retardation and acceleration of generic characters;” but I cannot follow the views of this eminent naturalist to their full extent. See Mr. Cope, “On the Origin of Genera,” from the ‘Proc. of Acad. Nat. Sc. of Philadelphia,’ Oct. 1868.

268 Jerdon, ‘Birds of India,’ vol. iii. p. 507, on the peacock. Audubon, ibid. vol. iii. p. 139, on the Ardea.

269 For illustrative cases see vol. iv. of Macgillivray’s ‘Hist. Brit. Birds;’ on Tringa, &c., p. 229, 271; on the Machetes, p. 172; on the Charadrius hiaticula, p. 118; on the Charadrius pluvialis, p. 94.

270 For the goldfinch of N. America, Fringilla tristis, Linn., see Audubon, ‘Ornith. Biography,’ vol. i. p. 172. For the Maluri, Gould’s 'Handbook of the Birds of Australia,’ vol. i. p. 318.

271 I am indebted to Mr. Blyth for information in regard to the Buphus; see also Jerdon, ‘Birds of India,’ vol. iii. p. 749. On the Anastomus, see Blyth, in ‘Ibis,’ 1867, p. 173.

272 On the Alca, see Macgillivray, ‘Hist. Brit. Birds,’ vol. v. p. 347. On the Fringilla leucophrys, Audubon, ibid. vol. ii. p. 89. I shall have hereafter to refer to the young of certain herons and egrets being white.

273 ‘History of British Birds,’ vol. i. 1839, p. 159.

274 Blyth, in Charlesworth’s ‘Mag. of Nat. Hist.’ vol. i. 1837, p. 362; and from information given to me by him.

275 Audubon, ‘Ornith. Biography,’ vol. i. p. 113.

276 Mr. C. A. Wright, in ‘Ibis,’ vol. vi. 1864, p. 65. Jerdon, ‘Birds of India,’ vol. i. p. 515.

277 The following additional cases may be mentioned: the young males of Tanagra rubra can be distinguished from the young females (Audubon, ‘Ornith. Biography,’ vol. iv. p. 392), and so it is with the nestlings of a blue nuthatch, Dendrophila frontalis of India (Jerdon, 'Birds of India,’ vol. i. p. 389). Mr. Blyth also informs me that the sexes of the stonechat, Saxicola rubicola, are distinguishable at a very early age.

278 ‘Westminster Review,’ July, 1867, p. 5.

279 ‘Ibis,’ 1859, vol. i. p. 429, et seq.

280 No satisfactory explanation has ever been offered of the immense size, and still less of the bright colours, of the toucan’s beak. Mr. Bates (‘The Naturalist on the Amazons,’ vol. ii. 1863, p. 341) states that they use their beak for reaching fruit at the extreme tips of the branches; and likewise, as stated by other authors, for extracting eggs and young birds from the nests of other birds. But as Mr. Bates admits, the beak “can scarcely be considered a very perfectly-formed instrument for the end to which it is applied.” The great bulk of the beak, as shewn by its breadth, depth, as well as length, is not intelligible on the view, that it serves merely as an organ of prehension.