Some facts may be noted respecting the characters of hybrids. In the first place, it is important to notice that the characters of the hybrid vary according to the sexes of the species concerned; thus, the “hinny,” which is bred from a horse and a she-ass, is a different animal from the true “mule,” which is bred from the jackass and mare, and is inferior to it.
Similarly, Mr G. E. Weston, a great authority on British cage-birds and their hybrids, informs us that when hybrids are bred from a male canary and a hen goldfinch or siskin—contrary to the almost universal practice of using the hen canary for crossing—the progeny are inferior in size and colour to the hybrids obtained in the ordinary way.
Hybrids, in animals at all events, differ from crosses between mutations or colour-variations in not exhibiting the phenomenon of alternative inheritance; they do not follow one parent or the other exclusively, but always exhibit some blending of the characters of both, which is, after all, what might have been expected, since well-defined species usually differ in more than one character.
Thus, the cross between the Amherst and gold pheasants chiefly resembles the latter, but has the ruff white as in the Amherst, while the crest, though in form it resembles that of the gold species, is not yellow as in that species, nor red as in the Amherst, but of an intermediate tint, brilliant orange.
The mule between the horse and ass, as all know, combines the shapes of the two parents, though in colour it follows the horse rather than the ass.
When two remote species, one or each of which possesses some distinctive structural peculiarity, are crossed, the hybrid does not inherit such points. The guinea-fowl has a helmet, and a pair of wattles on the upper jaw; the common fowl a comb, and a pair of wattles on the lower jaw; but in the hybrid no comb, helmet, or wattles are present.
The Muscovy drake has a bare red eye-patch, and the male of the common duck curled middle-tail feathers; in the hybrid neither of these peculiarities is reproduced.
In a cross between nearly-related forms, the peculiarity of one species may be reproduced in a modified form in the hybrid; for instance, in that between the blackcock (Tetrao tetrix) and the capercailzie (T. urogallus), the forked tail of the former reappears to a small extent in the hybrid.
Very interesting are those cases in which the hybrid resembles neither parent, but tends to be like an altogether distinct species, or to have a character of its own. Thus the hybrids between the pied European and chestnut African sheldrakes (Tadorna cornuta and Casarca cana), now in the British Museum, bear a distinct resemblance to the grey Australian sheldrake (C. tadornoides). In pheasants, also, the crosses between the common and gold, common and Amherst, gold and Japanese, and gold and Reeves’ pheasants, widely different as all these birds are in colouration, are remarkably alike, being all chestnut-coloured birds with buff median tail-feathers. These may be seen in the British Museum. This phenomenon, together with the above-noted disappearance of specialised features in hybrids, is possibly comparable to the “reversion” observed when widely-distinct domestic breeds are crossed, and so may give us an idea of the appearance of the ancestors of the groups of species concerned.
In the few cases wherein several generations of hybrids have been bred inter se, there seems to have been no reversion to the original pure types, such as happens when colour-forms are crossed.