363 In the common peacock (Pavo cristatus) the male alone possesses spurs, whilst both sexes of the Java peacock (P. muticus) offer the unusual case of being furnished with spurs. Hence I fully expected that in the latter species they would have been developed earlier in life than in the common peacock; but M. Hegt of Amsterdam informs me, that with young birds of the previous year, belonging to both species, compared on April 23rd, 1869, there was no difference in the development of the spurs. The spurs, however, were as yet represented merely by slight knobs or elevations. I presume that I should have been informed if any difference in the rate of development had subsequently been observed.

364 In some other species of the Duck Family the speculum in the two sexes differs in a greater degree; but I have not been able to discover whether its full development occurs later in life in the males of such species, than in the male of the common duck, as ought to be the case according to our rule. With the allied Mergus cucullatus we have, however, a case of this kind: the two sexes differ conspicuously in general plumage, and to a considerable degree in the speculum, which is pure white in the male and greyish-white in the female. Now the young males at first resemble, in all respects, the female, and have a greyish-white speculum, but this becomes pure white at an earlier age than that at which the adult male acquires his other more strongly-marked sexual differences in plumage: see Audubon, ‘Ornithological Biography,’ vol. iii. 1835, p. 249-250.

365 ‘Das Ganze der Taubenzucht,’ 1837, s. 21, 24. For the case of the streaked pigeons, see Dr. Chapuis, ‘Le Pigeon Voyageur Belge.’ 1865, p. 87.

366 For full particulars and references on all these points respecting the several breeds of the Fowl, see ‘Variation of Animals and Plants under Domestication,’ vol. i. p. 250, 256. In regard to the higher animals, the sexual differences which have arisen under domestication are described in the same work under the head of each species.

367 ‘Twenty-ninth Annual Report of the Registrar-General for 1866.’ In this report (p. xii) a special decennial table is given.

368 For Norway and Russia, see abstract of Prof. Faye’s researches, in ‘British and Foreign Medico-Chirurg. Review,’ April, 1867, p. 343, 345. For France, the ‘Annuaire pour l’An 1867.’ p. 213.

369 In regard to the Jews, see M. Thury, ‘La Loi de Production des Sexes,’ 1863, p. 25.

370 Babbage, ‘Edinburgh Journal of Science,’ 1829, vol. i. p. 88; also p. 90, on still-born children. On illegitimate children in England, see ‘Report of Registrar-General for 1866,’ p. xv.

371 ‘British and Foreign Medico-Chirurg. Review,’ April, 1867, p. 343. Dr. Stark also remarks (‘Tenth Annual Report of Births, Deaths, &c., in Scotland,’ 1867, p. xxviii) that “These examples may suffice to shew that, at almost every stage of life, the males in Scotland have a greater liability to death and a higher death-rate than the females. The fact, however, of this peculiarity being most strongly developed at that infantile period of life when the dress, food, and general treatment of both sexes are alike, seems to prove that the higher male death-rate is an impressed, natural, and constitutional peculiarity due to sex alone.”

372 With the savage Guaranys of Paraguay, according to the accurate Azara (‘Voyages dans l’Amérique mérid.’ tom. ii. 1809, p. 60, 179), the women in proportion to the men are as 14 to 13.

373 Leuckart in Wagner, ‘Handwörterbuch der Phys.’ B. iv. 1853, s. 774.

374 Anthropological Review, April, 1870, p. cviii.

375 During the last eleven years a record has been kept of the number of mares which have proved barren or prematurely slipped their foals; and it deserves notice, as shewing how infertile these highly-nurtured and rather closely-interbred animals have become, that not far from one-third of the mares failed to produce living foals. Thus during 1866, 809 male colts and 816 female colts were born, and 743 mares failed to produce offspring. During 1867, 836 males and 902 females were born, and 794 mares failed.

376 I am much indebted to Mr. Cupples for having procured for me the above returns from Scotland, as well as some of the following returns on cattle. Mr. R. Elliot, of Laighwood, first called my attention to the premature deaths of the males,—a statement subsequently confirmed by Mr. Aitchison and others. To this latter gentleman, and to Mr. Payan, I owe my thanks for the larger returns on sheep.

377 Bell, ‘History of British Quadrupeds,’ p. 100.

378 ‘Illustrations of the Zoology of S. Africa,’ 1849, pl. 29.

379 Brehm (‘Illust. Thierleben,’ B. iv. s. 990) comes to the same conclusion.

380 On the authority of L. Lloyd, ‘Game Birds of Sweden,’ 1867, p. 12, 132.

381 ‘Nat. Hist. of Selbourne,’ letter xxix. edit. of 1825, vol. i. p. 139.

382 Mr. Jenner Weir received similar information, on making enquiries during the following year. To shew the number of chaffinches caught, I may mention that in 1869 there was a match between two experts; and one man caught in a day 62, and another 40, male chaffinches. The greatest number ever caught by one man in a single day was 70.

383 ‘Ibis,’ vol. ii. p. 260, as quoted in Gould’s ‘Trochilidæ,’ 1861, p. 52. For the foregoing proportions, I am indebted to Mr. Salvin for a table of his results.

384 ‘Ibis,’ 1860, p. 137; and 1867, p. 369.

385 ‘Ibis,’ 1862, p. 137.

386 Leuckart quotes Bloch (Wagner, ‘Handwörterbuch der Phys.’ B. iv. 1853, s. 775), that with fish there are twice as many males as females.

387 Quoted in the ‘Farmer,’ March 18, 1869, p. 369.

388 ‘The Stormontfield Piscicultural Experiments,’ 1866, p. 23. The 'Field’ newspaper, June 29th, 1867.

389 ‘Land and Water,’ 1868, p. 41.

390 Yarrell, ‘Hist. British Fishes,’ vol. i. 1836, p. 307; on the Cyprinus carpio, p. 331; on the Tinca vulgaris, p. 331; on the Abramis brama, p. 336. See, for the minnow (Leuciscus phoxinus), ‘Loudon’s Mag. of Nat. Hist.’ vol. v. 1832, p. 682.

391 Leuckart quotes Meinecke (Wagner, ‘Handwörterbuch der Phys.’ B. iv. 1853, s. 775) that with Butterflies the males are three or four times as numerous as the females.

392 ‘The Naturalist on the Amazons,’ vol. ii. 1863, p. 228, 347.

393 Four of these cases are given by Mr. Trimen in his ‘Rhopalocera Africæ Australis.’

394 Quoted by Trimen, ‘Transact. Ent. Soc.’ vol. v. part iv. 1866, p. 330.

395 ‘Transact. Linn. Soc.’ vol. xxv. p. 37.

396 ‘Proc. Entomolog. Soc.’ Feb. 17th, 1868.

397 Quoted by Dr. Wallace in ‘Proc. Ent. Soc.’ 3rd series, vol. v. 1867, p. 487.

398 Blanchard, ‘Metamorphoses, Mœurs des Insectes,’ 1868, p. 225-226.

399 ‘Lepidopteren-Doubblettren Liste,’ Berlin, No. x. 1866.

400 This naturalist has been so kind as to send me some results from former years, in which the females seemed to preponderate; but so many of the figures were estimates, that I found it impossible to tabulate them.

401 Günther’s ‘Record of Zoological Literature,’ 1867, p. 260. On the excess of female Lucanus, ibid. p. 250. On the males of Lucanus in England, Westwood, ‘Modern Class. of Insects,’ vol. i. p. 187. On the Siagonium, ibid. p. 172.

402 Walsh, in ‘The American Entomologist,’ vol. i. 1869, p. 103. F. Smith, 'Record of Zoological Literature,’ 1867, p. 328.

403 ‘Farm Insects,’ p. 45-46.

404 ‘Observations on N. American Neuroptera,’ by H. Hagen and B. D. Walsh, ‘Proc. Ent. Soc. Philadelphia,’ Oct. 1863, p. 168, 223, 239.

405 ‘Proc. Ent. Soc. London,’ Feb. 17, 1868.

406 Another great authority in this class, Prof. Thorell of Upsala (‘On European Spiders,’ 1869-70, part i. p. 205) speaks as if female spiders were generally commoner than the males.

407 See, on this subject, Mr. Pickard-Cambridge, as quoted in ‘Quarterly Journal of Science,’ 1868, p. 429.

408 I have often been struck with the fact, that in several species of Primula the seeds in the capsules which contained only a few were very much larger than the numerous seeds in the more productive capsules.

409 ‘Principles of Biology,’ vol. ii. 1867, chaps. ii.-xi.

410 De l’Espèce et de la Class.’ &c., 1869, p. 106.

411 See, for instance, the account which I have given in my ‘Journal of Researches,’ 1845, p. 7.

412 I have given (‘Geolog. Observations on Volcanic Islands,’ 1844, p. 53) a curious instance of the influence of light on the colours of a frondescent incrustation, deposited by the surf on the coast-rocks of Ascension, and formed by the solution of triturated sea-shells.

413 ‘Facts and Arguments for Darwin,’ English translat. 1869, p. 20. See the previous discussion on the olfactory threads. Sars has described a somewhat analogous case (as quoted in ‘Nature,’ 1870, p. 455) in a Norwegian crustacean, the Pontoporeia affinis.

414 See Sir J. Lubbock in ‘Annals. and Mag. of Nat. Hist.’ vol. xi. 1853, pl. i. and x.; and vol. xii. (1853) pl. vii. See also Lubbock in 'Transact. Ent. Soc.’ vol. iv. new series, 1856-1858, p. 8. With respect to the zigzagged antennæ mentioned below, see Fritz Müller, ‘Facts and Arguments for Darwin’ 1869, p. 40, foot-note.

415 See a paper by Mr. C. Spence Bate, with figures, in ‘Proc. Zoolog. Soc.’ 1868, p. 363; and on the nomenclature of the genus, ibid. p. 585. I am greatly indebted to Mr. Spence Bate for nearly all the above statements with respect to the chelæ of the higher crustaceans.

416 ‘Hist. Nat. des Crust.’ tom. ii. 1837, p. 50.

417 Fritz Müller, ‘Facts and Arguments for Darwin,’ 1869, p. 25-28.

418 ‘Travels in the Interior of Brazil,’ 1846, p. 111. I have given, in my ‘Journal of Researches,’ p. 463, an account of the habits of the Birgos.

419 Mr. Ch. Fraser, in ‘Proc. Zoolog. Soc.’ 1869, p. 3. I am indebted to Mr. Bate for the statement from Dr. Power.

420 Claus, ‘Die freilebenden Copepoden,’ 1863, s. 35.

421 ‘Facts and Arguments,’ &c., p. 79.

422 ‘A History of the Spiders of Great Britain,’ 1861-64. For the following facts, see p. 102, 77, 88.

423 Aug. Vinson (‘Aranéides des Iles de la Réunion,’ pl. vi. figs. 1 and 2) gives a good instance of the small size of the male in Epeira nigra. In this species, as I may add, the male is testaceous and the female black with legs banded with red. Other even more striking cases of inequality in size between the sexes have been recorded (‘Quarterly Journal of Science,’ 1868, July, p. 429); but I have not seen the original accounts.

424 Kirby and Spence, ‘Introduction to Entomology,’ vol. i. 1818, p. 280.

425 Theridion (Asagena, Sund.) serratipes, 4-punctatum et guttatum; see Westring, in Kroyer, ‘Naturhist. Tidskrift,’ vol. iv. 1842-1843, p. 349; and vol. ii. 1846-1849, p. 342. See, also, for other species, 'Araneæ Svecicæ,’ p. 184.

426 Walckenaer et P. Gervais, ‘Hist. Nat. des Insectes: Aptères,’ tom. iv. 1847, p. 17, 19, 68.

427 Sir J. Lubbock, ‘Transact. Linnean Soc.’ vol. xxv. 1866, p. 484. With respect to the Mutillidæ see Westwood, ‘Modern Class. of Insects,’ vol. ii. p. 213.

428 These organs in the male often differ in closely-allied species, and afford excellent specific characters. But their importance, under a functional point of view, as Mr. E. MacLachlan has remarked to me, has probably been overrated. It has been suggested, that slight differences in these organs would suffice to prevent the intercrossing of well-marked varieties or incipient species, and would thus aid in their development. That this can hardly be the case, we may infer from the many recorded cases (see for instance, Bronn, ‘Geschichte der Natur,’ B. ii. 1843, s. 164; and Westwood, ‘Transact. Ent. Soc.’ vol. iii. 1842, p. 195) of distinct species having been observed in union. Mr. MacLachlan informs me (vide ‘Stett. Ent. Zeitung,’ 1867, s. 155) that when several species of Phryganidæ, which present strongly-pronounced differences of this kind, were confined together by Dr. Aug. Meyer, they coupled, and one pair produced fertile ova.

429 ‘The Practical Entomologist,’ Philadelphia, vol. ii. May, 1867, p. 88.

430 Mr. Walsh, ibid. p. 107.

431 ‘Modern Classification of Insects,’ vol. ii. 1840, p. 206, 205. Mr. Walsh, who called my attention to this double use of the jaws, says that he has repeatedly observed this fact.

432 We have here a curious and inexplicable case of dimorphism, for some of the females of four European species of Dytiscus, and of certain species of Hydroporus, have their elytra smooth; and no intermediate gradations between sulcated or punctured and quite smooth elytra have been observed. See Dr. H. Schaum, as quoted in the ‘Zoologist,’ vol. v.-vi. 1847-48, p. 1896. Also Kirby and Spence, ‘Introduction to Entomology,’ vol. iii. 1826, p. 305.

433 Westwood, ‘Modern Class.’ vol. ii. p. 193. The following statement about Penthe, and others in inverted commas, are taken from Mr. Walsh, ‘Practical Entomologist,’ Philadelphia, vol. ii. p. 88.

434 Kirby and Spence, ‘Introduct.’ &c., vol. iii. p. 332-336.

435 ‘Insecta Maderensia,’ 1854, p. 20.

436 E. Doubleday, ‘Annals and Mag. of Nat. Hist.’ vol. i. 1848, p. 379. I may add that the wings in certain Hymenoptera (see Shuckard, 'Fossorial Hymenop.’ 1837, p. 39-43) differ in neuration according to sex.

437 H. W. Bates, in ‘Journal of Proc. Linn. Soc.’ vol. vi. 1862, p. 74. Mr. Wonfor’s observations are quoted in ‘Popular Science Review,’ 1868, p. 343.

438 Kirby and Spence, ‘Introduction to Entomology,’ vol. iii. p. 299.

439 Robinet, ‘Vers à Soie,’ 1848, p. 207.

440 ‘Transact. Ent. Soc.’ 3rd series, vol. v. p. 486.

441 ‘Journal of Proc. Ent. Soc.’ Feb. 4th, 1867, p. lxxi.

442 For this and other statements on the size of the sexes, see Kirby and Spence, ibid. vol. iii. p. 300; on the duration of life in insects, see p. 344.

443 ‘Transact. Linnean Soc.’ vol. xxvi. 1868, p. 296.

444 ‘The Malay Archipelago,’ vol. ii. 1869, p. 313.

445 ‘Modern Classification of Insects,’ vol. ii. 1840, p. 526.

446 See Mr. B. T. Lowne’s very interesting work, ‘On the Anatomy of the Blow-Fly, Musca vomitoria,’ 1870, p. 14.

447 Westwood, ‘Modern Class. of Insects,’ vol. ii. p. 473.

448 These particulars are taken from Westwood’s ‘Modern Class. of Insects,’ vol. ii. 1840, p. 422. See, also, on the Fulgoridæ, Kirby and Spence, ‘Introduct.’ vol. ii. p. 401.

449 ‘Zeitschrift für wissenschaft. Zoolog.’ B. xvii. 1867, s. 152-158.

450 I am indebted to Mr. Walsh for having sent me this extract from a ‘Journal of the Doings of Cicada septemdecim,’ by Dr. Hartman.

451 L. Guilding, ‘Transact. Linn. Soc.’ vol. xv. p. 154.

452 Köppen, as quoted in the ‘Zoological Record,’ for 1867, p. 460.

453 Gilbert White, ‘Nat. Hist. of Selborne,’ vol. ii. 1825, p. 262.

454 Harris, ‘Insects of New England,’ 1842, p. 128.

455 ‘The Naturalist on the Amazons,’ vol. i. 1863, p. 252. Mr. Bates gives a very interesting discussion on the gradations in the musical apparatus of the three families. See also Westwood, ‘Modern Class.’ vol. ii. p. 445 and 453.

456 ‘Proc. Boston Soc. of Nat. Hist.’ vol. xi. April, 1868.

457 ‘Nouveau Manuel d’Anat. Comp.’ (French translat.), tom. i. 1850 p. 567.

458 ‘Zeitschrift für wissenschaft. Zoolog.’ B. xvii. 1867, s. 117.

459 Westwood, ‘Modern Class. of Insects,’ vol. i. p. 440.

460 Westwood, ‘Modern Class. of Insects,’ vol. i. p. 453.

461 Landois, ibid. s. 121, 122.

462 Mr. Walsh also informs me that he has noticed that the female of the Platyphyllum concavum, “when captured makes a feeble grating noise by shuffling her wing-covers together.”

463 Landois, ibid. s. 113.

464 ‘Insects of New England,’ 1842, p. 133.

465 Westwood, ‘Modern Classification,’ vol. i. p. 462.

466 Westwood, ibid. vol. i. p. 453.

467 Landois, ibid. s. 115, 116, 120, 122.

468 ‘Transact. Ent. Soc.’ 3rd series, vol. ii. (‘Journal of Proceedings, p. 117.)

469 Westwood, ‘Modern Class. of Insects,’ vol. i. p. 427; for crickets, p. 445.

470 Mr. Ch. Horne, in ‘Proc. Ent. Soc.’ May 3, 1869, p. xii.

471 The Oecanthus nivalis, Harris, ‘Insects of New England,’ 1842, p. 124.

472 Platyblemnus: Westwood, ‘Modern. Class.’ vol. i. p. 447.

473 B. D. Walsh, the Pseudo-neuroptera of Illinois, in ‘Proc. Ent. Soc. of Philadelphia,’ 1862, p. 361.

474 ‘Modern Class.’ vol. ii. p. 37.

475 Walsh, ibid. p. 381. I am indebted to this naturalist for the following facts on Hetærina, Anax, and Gomphus.

476 ‘Transact. Ent. Soc’ vol. i. 1836, p. lxxxi.

477 See abstract in the ‘Zoological Record’ for 1867, p. 450.

478 Kirby and Spence, ‘Introduct. to Entomology,’ vol. ii. 1818, p. 35.

479 See an interesting article, “The Writings of Fabre,” in ‘Nat. Hist. Review,’ April, 1862, p. 122.

480 ‘Journal of Proc. of Entomolog. Soc.’ Sept. 7th, 1863, p. 169.

481 P. Huber, ‘Recherches sur les Mœurs des Fourmis,’ 1810, p. 150, 165.

482 ‘Proc. Entomolog. Soc. of Philadelphia,’ 1866, p. 238-239.

483 Quoted by Westwood, ‘Modern Class. of Insects,’ vol. ii. p. 214.

484 Pyrodes pulcherrimus, in which the sexes differ conspicuously, has been described by Mr. Bates in ‘Transact. Ent. Soc.’ 1869, p. 50. I will specify the few other cases in which I have heard of a difference in colour between the sexes of beetles. Kirby and Spence (‘Introduct. to Entomology,’ vol. iii. p. 301) mention a Cantharis, Meloe, Rhagium, and the Leptura testacea; the male of the latter being testaceous, with a black thorax, and the female of a dull red all over. These two latter beetles belong to the Order of Longicorns. Messrs. R. Trimen and Waterhouse, junr., inform me of two Lamellicorns, viz., a Peritrichia and Trichius, the male of the latter being more obscurely coloured than the female. In Tillus elongatus the male is black, and the female always, as it is believed, of a dark blue colour with a red thorax. The male, also, of Orsodacna atra, as I hear from Mr. Walsh, is black, the female (the so-called O. ruficollis) having a rufous thorax.

485 ‘Proc. Entomolog. Soc. of Philadelphia,’ 1864, p. 228.

486 Kirby and Spence, ‘Introduct. Entomolog.’ vol. iii. p. 300.

487 Kirby and Spence, ibid. vol. iii. p. 329.

488 ‘Modern Classification of Insects,’ vol. i. p. 172. On the same page there is an account of Siagonium. In the British Museum I noticed one male specimen of Siagonium in an intermediate condition, so that the dimorphism is not strict.

489 ‘The Malay Archipelago,’ vol. ii. 1869, p. 276.

490 ‘Entomological Magazine,’ vol. i. 1833, p. 82. See also on the conflicts of this species, Kirby and Spence, ibid. vol. iii. p. 314; and Westwood, ibid. vol. i. p. 187.

491 Quoted from Fischer, in ‘Dict. Class. d’Hist. Nat.’ tom. x. p. 324.

492 ‘Ann. Soc. Entomolog. France,’ 1866, as quoted in ‘Journal of Travel,’ by A. Murray, 1868, p. 135.

493 Westwood, ‘Modern Class.’ vol. i. p. 184.

494 Wollaston, On certain musical Curculionidæ, ‘Annals and Mag. of Nat. Hist.’ vol. vi. 1860, p. 14.

495 ‘Zeitschrift für wiss. Zoolog.’ B. xvii. 1867, s. 127.

496 I am greatly indebted to Mr. G. R. Crotch for having sent me numerous prepared specimens of various beetles belonging to these three families and others, as well as for valuable information of all kinds. He believes that the power of stridulation in the Clythra has not been previously observed. I am also much indebted to Mr. E. W. Janson, for information and specimens. I may add that my son, Mr. F. Darwin, finds that Dermestes murinus stridulates, but he searched in vain for the apparatus. Scolytus has lately been described by Mr. Algen as a stridulator, in the ‘Edinburgh Monthly Magazine,’ 1869, Nov., p. 130.