EYE
INHERITED--DISEASES IN THE HORSE--LONGEVITY AND VIGOUR--ASYMMETRICAL
DEVIATIONS OF STRUCTURE--POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY
DIGITS AFTER AMPUTATION--CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED
FROM NON-AFFECTED PARENTS--WEAK AND FLUCTUATING INHERITANCE: IN WEEPING
TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS, COLOUR OF
HORSES--NON-INHERITANCE IN CERTAIN CASES--INHERITANCE OF STRUCTURE AND
HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY
RECURRING VARIABILITY, AND BY REVERSION--CONCLUSION.

The subject of inheritance is an immense one, and has been treated by many
authors. One work alone, 'De l'Heredite Naturelle,' by Dr. Prosper Lucas,
runs to the length of 1562 pages. We must confine ourselves to certain
points which have an important bearing on the general subject of variation,
both with domestic and natural productions. It is obvious that a variation
which is not inherited throws no light on the derivation of species, nor is
of any service to man, except in the case of perennial plants, which can be
propagated by buds.

If animals and plants had never been domesticated, and wild ones alone had
been observed, we should probably never have heard the saying, that "like
begets like." The proposition would have been as self-evident, as that all
the buds on the same tree are alike, though neither proposition is strictly
true. For, as has often been remarked, probably no two individuals are {2}
identically the same. All wild animals recognise each other, which shows
that there is some difference between them; and when the eye is well
practised, the shepherd knows each sheep, and man can distinguish a
fellow-man out of millions on millions of other men. Some authors have gone
so far as to maintain that the production of slight differences is as much
a necessary function of the powers of generation, as the production of
offspring like their parents. This view, as we shall see in a future
chapter, is not theoretically probable, though practically it holds good.
The saying that "like begets like" has in fact arisen from the perfect
confidence felt by breeders, that a superior or inferior animal will
generally reproduce its kind; but this very superiority or inferiority
shows that the individual in question has departed slightly from its type.

The whole subject of inheritance is wonderful. When a new character arises,
whatever its nature may be, it generally