A cross, which usually results in sterile offspring, may in very rare cases produce a fertile individual; thus, Mr A. Suchetet once succeeded in obtaining a three-quarter-bred bird from the not uncommon hybrid of the tame pigeon and tame collared dove (_Turtur risorius_), which is usually barren, by pairing it with a dove; but the bird thus produced, when again paired with a dove, was itself sterile. Some of the cases here given seem to encourage Darwin’s view that domestication tends to eliminate sterility; but it is doubtful if this can be upheld. The hybrid between the Muscovy duck (_Cairina moschata_) and common duck is usually, at all events, sterile, like that between the pigeon and dove; yet all these birds have been long domesticated. The hybrid between the fowl and the guinea-fowl is likewise barren, nor has the long domestication of the horse and ass lessened the sterility of the mule. Characters of Hybrids 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.