ids are apt to be extremely double.

[437] 'Teoria della Riproduzione Veg.,' 1816, p. 73.

[438] 'Bastarderzeugung,' s. 573.

[439] Ibid., s. 527.

[440] 'Transactions Phil. Soc.,' 1799, p. 202. For Koelreuter, _see_ 'Mem.
de l'Acad. de St. Petersbourg,' tom. iii., 1809 (published 1811), p. 197.
In reading C. K. Sprengel's remarkable work, 'Das entdeckte Geheimniss,'
&c., 1793, it is curious to observe how often this wonderfully acute
observer failed to understand the full meaning of the structure of the
flowers which he has so well described, from not always having before his
mind the key to the problem, namely, the good derived from the crossing of
distinct individual plants.

[441] This abstract was published in the fourth edition (1866) of my
'Origin of Species;' but as this edition will be in the hands of but few
persons, and as my original observations on this point have not as yet been
published in detail, I have ventured here to reprint the abstract.

[442] The term _unconscious selection_ has been objected to as a
contradiction: but _see_ some excellent observations on this head by Prof.
Huxley ('Nat. Hist. Review,' Oct. 1864, p. 578), who remarks that when the
wind heaps up sand-dunes it sifts and _unconsciously selects_ from the
gravel on the beach grains of sand of equal size.

[443] Sheep, 1838, p. 60.

[444] Mr. J. Wright on Shorthorn Cattle, in 'Journal of Royal Agricult.
Soc.,' vol. vii. pp. 208, 209.

[445] H. D. Richardson on Pigs, 1817, p. 44.

[446] 'Journal of R. Agricult. Soc.,' vol. i. p. 24.

[447] Sheep, pp. 520, 319.

[448] Loudon's 'Mag. of Nat. Hist.,' vol. viii., 1835, p. 618.

[449] 'A Treatise on the Art of Breeding the Almond Tumbler,' 1851, p. 9.

[450] 'Recreations in Agriculture,' vol. ii. p. 409.

[451] Youatt on Cattle, pp. 191, 227.

[452] Ferguson, 'Prize Poultry,' 1854, p. 208.

[453] Wilson, in 'Transact. Highland Agricult. Soc.,' quoted in 'Gard.
Chronicle,' 1844, p. 29.

[454] Simmonds, quoted in 'Gard. Chronicle,' 1855, p. 637. And for the
second quotation, _see_ Youatt on Sheep, p. 171.

[455] Robinet, 'Vers a Soie,' 1848, p. 271.

[456] Quatrefages, 'Les Maladies du Ver a Soie,' 1859, p. 101.

[457] M. Simon, in 'Bull. de la Soc. d'Acclimat.,' tom. ix., 1862, p. 221.

[458] 'The Poultry Chronicle,' vol. i., 1854, p. 607.

[459] J. M. Eaton, 'A Treatise on Fancy Pigeons,' 1852, p. xiv., and 'A
Treatise on the Almond Tumbler,' 1851, p. 11.

[460] '