ides_ 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 earlier chapters, that some of our domesticated
animals, such as dogs, cattle, pigs, &c., are almost certainly descended
from more than one species, or wild race, if any one prefers to apply this
latter term to forms which were enabled to keep distinct in a state of
nature. Hence the crossing of aboriginally distinct species probably came
into play at an early period in the formation of our present races. From
Ruetimeyer's observations there can be little doubt that this occurred with
cattle; but in most cases some one of the forms which were allowed to cross
freely, will, it is probable, have absorbed and obliterated the others. For
it is not likely that semi-civilized 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 in the formation or
modification of our races. It is not yet known whether the species of
silk-moth which have been recently crossed in France will yield permanent
races. In the fourth chapter I alluded with some hesitation to the
statement that a new breed, between the hare and rabbit, called leporides,
had been formed in France, and was found capable of propagating {99}
itself; but it is now positively affirmed[213] that this is an error. With
plants which can be multiplied by buds and cuttings, hybridisation has done
wonders, as with many kinds of Roses, Rhododendrons, Pelargoniums,
Calceolarias, and Petunias. Nearly all these plants can be propagated by
seed; most of them freely; but extremely few or none come true by seed.

Some authors believe that crossing is the chief cause of variability,--that
is, of the appearance of absolutely new characters. Some have gone so far
as to look at it as the sole cause; but this conclusion is disproved by
some of the facts given in the chapter on Bud-variation. The belief that
characters not present in either parent or in their ancestors