il and elevation of each district, and varies
with the season; and as new varieties have often been imported from abroad,
can we feel sure that our kidney-beans are not somewhat hardier? I have not
been able, by searching old horticultural works, to answer this question
satisfactorily.

On the whole the facts now given show that, though habit does something
towards acclimatisation, yet that the spontaneous appearance of
constitutionally different individuals is a far more effective agent. As no
single instance has been recorded, either with animals or plants, of
hardier individuals {315} having been long and steadily selected, though
such selection is admitted to be indispensable for the improvement of any
other character, it is not surprising that man has done little in the
acclimatisation of domesticated animals and cultivated plants. We need not,
however, doubt that under nature new races and new species would become
adapted to widely different climates, by spontaneous variation, aided by
habit, and regulated by natural selection.

_Arrests of Development: Rudimentary and Aborted Organs._

These subjects are here introduced because there is reason to believe
that rudimentary organs are in many cases the result of disuse.
Modifications of structure from arrested development, so great or so
serious as to deserve to be called monstrosities, are of common
occurrence, but, as they differ much from any normal structure, they
require here only a passing notice. When a part or organ is arrested
during its embryonic growth, a rudiment is generally left. Thus the
whole head may be represented by a soft nipple-like projection, and the
limbs by mere papillae. These rudiments of limbs are sometimes
inherited, as has been observed in a dog.[796]

Many lesser anomalies in our domesticated animals appear to be due to
arrested development. What the cause of the arrest may be, we seldom
know, except in the case of direct injury to the embryo within the egg
or womb. That the cause does not generally act at a very early
embryonic period we may infer from the affected organ seldom being
wholly aborted,--a rudiment being generally preserved. The external
ears are represented by mere vestiges in a Chinese breed of sheep; and
in another breed, the tail is reduced "to a little button, suffocated,
in a manner, by fat."[797] In tailless dogs and cats a stump is left;