onuments, by which we learn that the order of things which how reigns
in each place has not always prevailed, and by inference anticipate that
it will not always continue the same.[794]

Every considerable alteration in the local circumstances in which each
race of animals exists causes a change in their wants, and these new
wants excite them to new actions and habits. These actions require the
more frequent employment of some parts before but slightly exercised,
and then greater development follows as a consequence of their more
frequent use. Other organs no longer in use are impoverished and
diminished in size, nay, are sometimes entirely annihilated, while in
their place new parts are insensibly produced for the discharge of new
functions.[795]

I must here interrupt the author's argument, by observing, that no
positive fact is cited to exemplify the substitution of some _entirely
new_ sense, faculty, or organ, in the room of some other suppressed as
useless. All the instances adduced go only to prove that the dimensions
and strength of members and the perfection of certain attributes may, in
a long succession of generations, be lessened and enfeebled by disuse;
or, on the contrary, be matured and augmented by active exertion; just
as we know that the power of scent is feeble in the greyhound, while its
swiftness of pace and its acuteness of sight are remarkable--that the
harrier and stag-hound, on the contrary, are comparatively slow in their
movements, but excel in the sense of smelling.

It was necessary to point out to the reader this important chasm in the
chain of evidence, because he might otherwise imagine that I had merely
omitted the illustrations for the sake of brevity; but the plain truth
is, that there were no examples to be found; and when Lamarck talks "of
the efforts of internal sentiment," "the influence of subtle fluids,"
and "acts of organization," as causes whereby animals and plants may
acquire _new organs_, he substitutes names for things; and, with a
disregard to the strict rules of induction, resorts to fictions, as
ideal as the "plastic virtue," and other phantoms of the geologists of
the middle ages.

It is evident that, if some well-authenticated facts could have been
adduced to establish one complete step in the process of transformation,
such as the appearance, in individuals descending from a common stock,
of a sense or organ entirely new, and a complete disappearance of some
other