instance, of the woodpecker, with its feet, tail, beak, and tongue, so
admirably adapted to catch insects under the bark of trees. In the case of
the mistletoe, which draws its nourishment from certain trees, which has
seeds that must be transported by certain birds, and which has flowers with
separate sexes absolutely requiring the agency of certain insects to bring
pollen from one flower to the other, it is equally preposterous to account
for the structure of this parasite, with its relations to several distinct
organic beings, by the effects of external conditions, or of habit, or of
the volition of the plant itself.

It is, therefore, of the highest importance to gain a clear insight into
the means of modification and coadaptation. At the commencement of my
observations it seemed to me probable that a careful study of domesticated
animals and of cultivated plants would offer the best chance of making out
this obscure problem. Nor have I been disappointed; in this and in all
other perplexing cases I have invariably found that our knowledge,
imperfect though it be, of variation under domestication, afforded the best
and safest clue. I may venture to express my conviction of the high value
of such studies, although they have been very commonly neglected by
naturalists.

>From these considerations, I shall devote the first chapter of this
abstract to variation under domestication. We shall thus see that a large
amount of hereditary modification is at least possible; and, what is
equally or more important, we shall see how great is the power of man in
accumulating by his selection successive slight variations. I will then
pass on to the variability of species in a state of nature; but I shall,
unfortunately, be compelled to treat this subject far too briefly, as it
can be treated properly only by giving long catalogues of facts. We shall,
however, be enabled to discuss what circumstances are most favourable to