Inequalities in the two sides of the body, though opposed to the law of
symmetry, may be transmitted. There is ample evidence that the effects of
mutilations and of accidents, especially or perhaps exclusively when followed
by disease, are occasionally inherited. There can be no doubt that the evil
effects of the long-continued exposure of the parent to injurious conditions
are sometimes transmitted to the offspring. So it is, as we shall see in a
future chapter, with the effects of the use and disuse of parts, and of mental
habits. Periodical habits are likewise transmitted, but generally, as it would
appear, with little force.

Hence we are led to look at inheritance as the rule, and non-inheritance as
the anomaly. But this power often appears to us in our ignorance to act
capriciously, transmitting a character with inexplicable strength or
feebleness. The very same peculiarity, as the weeping habit of trees, silky
feathers, etc., may be inherited either firmly or not at all by different
members of the same group, and even by different individuals of the same
species, though treated in the same manner. In this latter case we see that
the power of transmission is a quality which is merely individual in its
attachment. As with single characters, so it is with the several concurrent
slight differences which distinguish sub-varieties or races; for of these,
some can be propagated almost as truly as species, whilst others cannot be
relied on. The same rule holds good with plants, when propagated by bulbs,
offsets, etc., which in one sense still form parts of the same individual, for
some varieties retain or inherit through successive bud-generations their
character far more truly than others.

Some characters not proper to the parent-species have certainly been inherited
from an extremely remote epoch, and may therefore be considered as firmly
fixed. But it is doubtful whether length of inheritance in itself gives
fixedness of character; though the chances are obviously in favour of any