Thus I raised several chickens from a Polish hen by a Spanish cock,--breeds which do not incubate,--and none of the young hens at first showed any tendency to sit; but one of them--the only one which was preserved--in the third year sat well on her eggs and reared a brood of chickens. So that here we have the reappearance with advancing age of a primitive instinct, in the same manner as we have seen that the red plumage of the Gallus bankiva is sometimes reacquired both by crossed and purely-bred fowls of various kinds as they grow old.
The parents of all our domesticated animals were of course aboriginally wild in disposition; and when a domesticated species is crossed with a distinct species, whether this is a domesticated or only a tamed animal, the hybrids are often wild to such a degree, that the fact is intelligible only on the principle that the cross has caused a partial return to a primitive disposition. Thus, the Earl of Powis formerly imported some thoroughly domesticated humped cattle from India, and crossed them with English breeds, which belong to a distinct species; and his agent remarked to me, without any question having been asked, how oddly wild the cross-bred animals were. The European wild boar and the Chinese domesticated pig are almost certainly specifically distinct: Sir F. Darwin crossed a sow of the latter breed with a wild Alpine boar which had become extremely tame, but the young, though having half-domesticated blood in their veins, were "extremely wild in confinement, and would not eat swill like common English pigs." Captain Hutton, in India, crossed a tame goat with a wild one from the Himalaya, and he remarked to me how surprisingly wild the offspring were. Mr. Hewitt, who has had great experience in crossing tame cock-pheasants with fowls belonging to five breeds, gives as the character of all "extraordinary wildness" (13/42. 'The Poultry Book' by Tegetmeier 1866 pages 165, 167.); but I have myself seen one exception to this rule. Mr. S. J. Salter (13/43. 'Natural History Review' 1863 April page 277.) who raised a large number of hybrids from a bantam-hen by Gallus sonneratii, states that "all were exceedingly wild." Mr. Waterton (13/44. 'Essays on Natural History' page 917.) bred some wild ducks from eggs hatched under a common duck, and the young were allowed to cross freely both amongst themselves and with the tame ducks; they were "half wild and half tame; they came to the windows to be fed, but still they had a wariness about them quite remarkable."
On the other hand, mules from the horse and ass are certainly not in the least wild, though notorious for obstinacy and vice. Mr. Brent, who has crossed canary-birds with many kinds of finches, has not observed, as he informs me, that the hybrids were in any way remarkably wild: but Mr. Jenner Weir who has had still greater experience, is of a directly opposite opinion. He remarks that the siskin is the tamest of finches, but its mules are as wild, when young, as newly caught birds, and are often lost through their continued efforts to escape. Hybrids are often raised between the common and musk duck, and I have been assured by three persons, who have kept these crossed birds, that they were not wild; but Mr. Garnett (13/45. As stated by Mr. Orton in his 'Physiology of Breeding' page 12.) observed that his hybrids were wild, and exhibited "migratory propensities" of which there is not a vestige in the common or musk duck. No case is known of this latter bird having escaped and become wild in Europe or Asia, except, according to Pallas, on the Caspian Sea; and the common domestic duck only occasionally becomes wild in districts where large lakes and fens abound. Nevertheless, a large number of cases have been recorded (13/46. M. E. de Selys-Longchamps refers ('Bulletin Acad. Roy. de Bruxelles' tome 12 No. 10) to more than seven of these hybrids shot in Switzerland and France. M. Deby asserts ('Zoologist' volume 5 1845-46 page 1254) that several have been shot in various parts of Belgium and Northern France.