[18] With respect to feral pigeons—for Juan Fernandez, _ see_ Bertero in ‘Annal. des Sc. Nat.,’ tom. xxi. p. 351. For Norfolk Islands, _see_ Rev. E. S. Dixon in the ‘Dovecote,’ 1851, p. 14, on the authority of Mr. Gould. For Ascension I rely on MS. information given me by Mr. Layard. For the banks of the Hudson, _see_ Blyth in ‘Annals of Nat. Hist.,’ vol. xx., 1857, p. 511. For Scotland, _see_ Macgillivray, ‘British Birds,’ vol. i. p. 275; also Thompson’s ‘Nat. Hist. of Ireland, Birds,’ vol. ii. p. 11. For ducks, _see_ Rev. E. S. Dixon, ‘Ornamental Poultry,’ 1847, p. 122. For the feral hybrids of the common and musk-ducks, _see_ Audubon’s ‘American Ornithology,’ and Selys-Longchamp’s ‘Hybrides dans la Famille des Anatides.’ For the goose, Isidore Geoffroy St.-Hilaire, ‘Hist. Nat. Gén.,’ tom. iii. p. 498. For guinea-fowls, _see_ Gosse’s ‘Naturalist’s Sojourn in Jamaica,’ p. 124; and his ‘Birds of Jamaica,’ for fuller particulars. I saw the wild guinea-fowl in Ascension. For the peacock, _see_ ‘A Week at Port Royal,’ by a competent authority, Mr. R. Hill, p. 42. For the turkey I rely on oral information; I ascertained that they were not Curassows. With respect to fowls I will give the references in the next chapter. [19] I have drawn out a long table of the various crosses made by fanciers between the several domestic breeds but I do not think it worth while publishing. I have myself made for this special purpose many crosses, and all were perfectly fertile. I have united in one bird five of the most distinct races, and with patience I might undoubtedly have thus united all. The case of five distinct breeds being blended together with unimpaired fertility is important, because Gärtner has shown that it is a very general, though not, as he thought, universal rule, that complex crosses between several species are excessively sterile. I have met with only two or three cases of reported sterility in the offspring of certain races when crossed. Pistor (‘Das Ganze der Feldtaubenzucht,’ 1831, s. 15) asserts that the mongrels from Barbs and Fantails are sterile: I have proved this to be erroneous, not only by crossing those hybrids with several other hybrids of the same parentage, but by the more severe test of pairing brother and sister hybrids _inter se,_ and they were _perfectly_ fertile. Temminck has stated (‘Hist. Nat. Gén. des Pigeons,’ tom. i. p. 197) that the Turbit or Owl will not cross readily with other breeds: but my Turbits crossed, when left free with Almond Tumblers and with Trumpeters; the same thing has occurred (Rev. E. S. Dixon, ‘The Dovecote,’ p. 107) between Turbits and Dovecots and Nuns. I have crossed Turbits with Barbs, as has M. Boitard (p. 34), who says the hybrids were very fertile. Hybrids from a Turbit and Fantail have been known to breed _inter se_ (Riedel, ‘Taubenzucht,’ s. 25, and Bechstein, ‘Naturgesch. Deutsch.,’ B. iv. s. 44. Turbits (Riedel, s.