occasionally produced by pure breeds of various colours and that when this
occurs certain black marks invariably appear on the wings and tail; so
again, when variously coloured breeds are crossed, blue birds with the same
black marks are frequently produced. We shall further see that these facts
are explained by, and afford strong evidence in favour of, the view that
all the breeds are descended from the rock-pigeon, or Columba livia, which
is thus coloured and marked. But the appearance of the stripes on the
various breeds of the horse, when of a dun colour, does not afford nearly
such good evidence of their descent from a single primitive stock as in the
case of the pigeon: because no horse certainly wild is known as a standard
of comparison; because the stripes when they appear are variable in
character; because there is far from sufficient evidence that the crossing
of distinct breeds produces stripes, and lastly, because all the species of
the genus Equus have the spinal stripe, and several species have shoulder
and leg stripes. Nevertheless the similarity in the most distinct breeds in
their general range of colour, in their dappling, and in the occasional
appearance, especially in duns, of leg-stripes and of double or triple
shoulder-stripes, taken together, indicate the probability of the descent
of all the existing races from a single, dun-coloured, more or less
striped, primitive stock, to which our horses occasionally revert.

THE ASS.

Four species of Asses, besides three zebras, have been described by
naturalists. There is now little doubt that our domesticated animal is
descended from the Equus taeniopus of Abyssinia. (2/43. Dr. Sclater in
'Proc. Zoolog. Soc.' 1862 page 164. Dr. Hartmann says ('Annalen der Landw.'
b. 44 page 222) that this animal in its wild state is not always striped
across the legs.) The ass is sometimes advanced as an instance of an animal
domesticated, as we know by the Old Testament, from an ancient period,