lightly altered from their usual form, size, or other
characters: and many of the peculiarities thus acquired are transmitted
to their offspring. Thus in animals, the size and vigour of body,
fatness, period of maturity, habits of body or consensual movements,
habits of mind and temper, are modified or acquired during the life of
the individual{187}, and become inherited. There is reason to believe
that when long exercise has given to certain muscles great development,
or disuse has lessened them, that such development is also inherited.
Food and climate will occasionally produce changes in the colour and
texture of the external coverings of animals; and certain unknown
conditions affect the horns of cattle in parts of Abyssinia; but whether
these peculiarities, thus acquired during individual lives, have been
inherited, I do not know. It appears certain that malconformation and
lameness in horses, produced by too much work on hard roads,--that
affections of the eyes in this animal probably caused by bad
ventilation,--that tendencies towards many diseases in man, such as
gout, caused by the course of life and ultimately producing changes of
structure, and that many other diseases produced by unknown agencies,
such as goitre, and the idiotcy resulting from it, all become
hereditary.

{186} The cumulative effect of domestication is insisted on in the
_Origin_, see _e.g. Origin_, Ed. i. p. 7, vi. p. 8.

{187} This type of variation passes into what he describes as the
direct effect of conditions. Since they are due to causes acting
during the adult life of the organism they might be called
individual variations, but he uses this term for congenital
variations, _e.g._ the differences discoverable in plants raised
from seeds of the same pod _(Origin_, Ed. i. p. 45, vi. p. 53).

It is very doubtful whether the flowers and leaf-buds, annually produced
from the same bulb, root, or tree, can properly be considered as parts
of the same individual, though in some respects they certainly seem to
be so. If they are parts of an individual, plants also are subject to
considerable changes during their _individual_ lives. Most
florist-flowers if neglected degenerate, that is, they lose some of
their characters; so common is this, that trueness is often stated, as
greatly enhancing the value of a variety{188}: tulips break their
colours only after some years' culture; some plants become double an