ses by insensible shades
into something else; that even the more remarkable differences are
evanescent, and that nature has, for the most part, left us nothing at
our disposal for establishing distinctions, save trifling, and, in some
respects, puerile particularities.

We find that many genera amongst animals and plants are of such an
extent, in consequence of the number of species referred to them, that
the study and determination of these last has become almost
impracticable. When the species are arranged in a series, and placed
near to each other, with due regard to their natural affinities, they
each differ in so minute a degree from those next adjoining, that they
almost melt into each other, and are in a manner confounded together. If
we see isolated species, we may presume the absence of some more closely
connected, and which have not yet been discovered. Already are there
genera, and even entire orders--nay, whole classes, which present an
approximation to the state of things here indicated.

If, when species have been thus placed in a regular series, we select
one, and then, making a leap over several intermediate ones, we take a
second, at some distance from the first, these two will, on comparison,
be seen to be very dissimilar; and it is in this manner that every
naturalist begins to study the objects which are at his own door. He
then finds it an easy task to establish generic and specific
distinctions; and it is only when his experience is enlarged, and when
he has made himself master of the intermediate links, that his
difficulties and ambiguities begin. But while we are thus compelled to
resort to trifling and minute characters in our attempt to separate the
species, we find a striking disparity between individuals which we know
to have descended from a common stock; and these newly acquired
peculiarities are regularly transmitted from one generation to another,
constituting what are called _races_.

From a great number of facts, continues the author, we learn that in
proportion as the individuals of one of our species change their
situation, climate, and manner of living, they change also, by little
and little, the consistence and proportions of their parts, their form,
their faculties, and even their organization, in such a manner that
every thing in them comes at last to participate in the mutations to
which they have been exposed. Even in the same climate, a great
difference of situation and expo