w, I think, that in every department of nature
there occur instances of the instability of specific form, which the
increase of materials aggravates rather than diminishes. And it must be
remembered that the naturalist is rarely likely to err on the side of
imputing greater indefiniteness to species than really exists. There is
a completeness and satisfaction to the mind in defining and limiting
and naming a species, which leads us all to do so whenever we
conscientiously can, and which we know has led many collectors to reject
vague intermediate forms as destroying the symmetry of their cabinets.
We must therefore consider these cases of excessive variation and
instability as being thoroughly well established; and to the objection
that, after all, these cases are but few compared with those in which
species can be limited and defined, and are therefore merely exceptions
to a general rule, I reply that a true law embraces all apparent
exceptions, and that to the great laws of nature there are no real
exceptions--that what appear to be such are equally results of law, and
are often (perhaps indeed always) those very results which are most
important as revealing the true nature and action of the law. It is for
such reasons that naturalists now look upon the study of _varieties_ as
more important than that of well-fixed species. It is in the former that
we see nature still at work, in the very act of producing those
wonderful modifications of form, that endless variety of colour, and
that complicated harmony of relations, which gratify every sense and
give occupation to every faculty of the true lover of nature.

_Variation as specially influenced by Locality._

The phenomena of variation as influenced by locality have not hitherto
received much attention. Botanists, it is true, are acquainted with the
influences of climate, altitude, and other physical conditions, in
modifying the forms and external characteristics of plants; but I am not
aware that any peculiar influence has been traced to locality,
independent of climate. Almost the only case I can find recorded is
mentioned in that repertory of natural-history facts, "The Origin of
Species," viz. that herbaceous groups have a tendency to become arboreal
in islands. In the animal world, I cannot find that any facts have been
pointed out as showing the special influence of locality in giving a
peculiar _facies_ to the several disconnected species that inhabit it.
What