Penguins; afterwards most of the ducks reared during three generations were
nearly uniform in character, being brown with a white crescentic mark on the
lower part of the breast, and with some white spots at the base of the beak;
so that by the aid of a little selection a new breed might easily have been
formed. With regard to crossed varieties of plants, Mr. Beaton (15/33.
'Cottage Gardener' 1856 page 110.) remarks that "Melville's extraordinary
cross between the Scotch kale and an early cabbage is as true and genuine as
any on record;" but in this case no doubt selection was practised. Gartner
(15/34. 'Bastarderzeugung' s. 553.) has given five cases of hybrids, in which
the progeny kept constant; and hybrids between Dianthus armeria and deltoides
remained true and uniform to the tenth generation. Dr. Herbert likewise showed
me a hybrid from two species of Loasa which from its first production had kept
constant during several generations.

We have seen in the first chapter, that the several kinds of dogs are almost
certainly descended from more than one species, and so it is with cattle, pigs
and some other domesticated animals. Hence the crossing of aboriginally
distinct species probably came into play at an early period in the formation
of our present races. From Rutimeyer's observations there can be little doubt
that this occurred with cattle; but in most cases one form will probably have
absorbed and obliterated the other, for it is not likely that semi-civilised
men would have taken the necessary pains to modify by selection their
commingled, crossed, and fluctuating stock. Nevertheless, those animals which
were best adapted to their conditions of life would have survived through
natural selection; and by this means crossing will often have indirectly aided
in the formation of primeval domesticated breeds. Within recent times, as far
as animals are concerned, the crossing of distinct species has done little or
nothing towards the formation or modification of our races. It is not yet
known whether the several species of silk-moth which have been recently
crossed in France will yield permanent races. With plants which can be