se and disuse, combined with natural
selection; organs of flight and of vision--Acclimatisation--Correlation
of growth--Compensation and economy of growth--False
correlations--Multiple, rudimentary, and lowly organised structures
variable--Parts developed in an unusual manner are highly variable:
specific characters more variable than generic: secondary sexual
characters variable--Species of the same genus vary in an analogous
manner--Reversions to long-lost characters--Summary.

I have hitherto sometimes spoken as if the variations--so common and
multiform in organic beings under domestication, and in a lesser degree in
those in a state of nature--had been due to chance. This, of course, is a
wholly incorrect expression, but it serves to acknowledge plainly our
ignorance of the cause of each particular variation. Some authors believe
it to be as much the function of the reproductive system to produce
individual differences, or very slight deviations of structure, as to make
the child like its parents. But the much greater variability, as well as
the greater frequency of monstrosities, under domestication or cultivation,
than under nature, leads me to believe that deviations of structure are in
some way due to the nature of the conditions of life, to which the parents
and their more remote ancestors have been exposed during several
generations. I have remarked in the first chapter--but a long catalogue of
facts which cannot be here given would be necessary to show the truth of
the remark--that the reproductive system is eminently susceptible to
changes in the conditions of life; and to {132} this system being
functionally disturbed in the parents, I chiefly attribute the varying or
plastic condition of the offspring. The male and female sexual elements
seem to be affected before that union takes place which is to form a new
being. In the case of "sporting" plants, the bud, which in its earliest
condition does not apparently differ essentially from an ovule, is alone
affected. But why, because the reproductive system is disturbed, this or
that part should vary more or less, we are profoundly ignorant.
Nevertheless, we can here and there dimly catch a faint ray of light, and
we may feel sure that there must be some cause for each deviation of
structure, however slight.

How much direct effect difference of climate, food, &c., produces on any
being is extremely doubtful. My impression is, that t