Among wild ruminants of this hollow-horned family, the Himalayan Argali (_Ovis ammon_) ram, a giant sheep of the size of a donkey, has been known to appropriate a herd of ewes of the Urial (_O. vignei_), a very distinct species of the size of a domestic sheep. Many hybrids were born, and these, in turn, bred with the pure urials of the herd. In our parks the little Sika deer of Japan (_Cervus sika_), a species about the size of the fallow-deer, with an even more marked seasonal change of colouration and antlers having only three tines, breeds with the red deer, and the hybrids are fertile. In certain parts of Asia Minor the natives cross the female one-humped camel with the male of the bactrian or two-humped species. The hybrids (which are one-humped) will breed with the pure species; but, although the hybrids are strong and useful, the three-quarter bred beasts are apparently of little value. Fertile Bird Hybrids Coming to birds, we are confronted by a longer list of fertile hybrids. This is the natural outcome of the fact that a greater number of bird species have been kept in captivity. The oldest known fertile hybrid is that between the common and Chinese geese above cited, but many others have since been recorded. Even among birds so seldom bred, comparatively, as the parrot family, a fertile hybrid has been produced, that between the Australian Rosella Parrakeet (_Platycercus eximius_) and Pennant’s Parrakeet (_P. elegans_). The hybrid was first described as a distinct species, the Red-mantled Parrakeet (_P. erythropeplus_). These two parrakeets, though nearly allied, are very distinct; Pennant’s being coloured red, blue, and black, with a distinct young plumage of uniform dull green; the rosella in addition to the above colours displays much yellow and some white and green. It is, moreover, considerably smaller and has no distinct youthful dress. The Amherst Pheasant (_Chrysolophus amherstiæ_) and the Gold Pheasant (_C. pictus_) have long been known as producing hybrids which are fertile either _inter se_ or with the parents. Here the species are still more distinct; not only are the leading colours of the Amherst white and green, instead of red and gold, but it is a bigger bird with a larger tail and smaller crest, and a bare patch round the eyes. The Pintail Duck (_Dafila acuta_) and the Mallard or Wild Duck and its domestic descendants (_Anas boscas_), when bred together, produce hybrids which have been proved fertile between themselves and with the pure pintail. Any sportsman or frequenter of our parks can see for himself the distinctness of the species concerned. The Pied Wagtail (_Motacilla lugubris_) and the Grey Wagtail (_M. melanope_) have produced hybrids in aviaries, which have proved fertile. The two species are distinct in every way, as all British ornithologists know.