nimate world, and the capability of the species to be indefinitely
modified by the influence of external circumstances. Henceforth his
speculations know no definite bounds; he gives the rein to conjecture,
and fancies that the outward form, internal structure, instinctive
faculties, nay, that reason itself may have been gradually developed
from some of the simplest states of existence--that all animals, that
man himself, and the irrational beings, may have had one common origin;
that all may be parts of one continuous and progressive scheme of
development, from the most imperfect to the more complex; in fine, he
renounces his belief in the high genealogy of his species, and looks
forward, as if in compensation, to the future perfectibility of man in
his physical, intellectual, and moral attributes.

Let us now proceed to consider what is defective in evidence, and what
fallacious in reasoning, in the grounds of these strange conclusions.
Blumenbach judiciously observes, that "no general rule can be laid down
for determining the distinctness of species, as there is no particular
class of characters which can serve as a criterion. In each case we must
be guided by _analogy_ and _probability_." The multitude, in fact, and
complexity of the proofs to be weighed is so great, that we can only
hope to obtain presumptive evidence, and we must, therefore, be the more
careful to derive our general views as much as possible from those
observations where the chances of deception are least. We must be on our
guard not to tread in the footsteps of the naturalists of the middle
ages, who believed the doctrine of spontaneous generation to be
applicable to all those parts of the animal and vegetable kingdoms which
they least understood, in direct contradiction to the analogy of all the
parts best known to them; and who, when at length they found that
insects and cryptogamous plants were also propagated from eggs or seeds,
still persisted in retaining their old prejudices respecting the
infusory animalcules and other minute beings, the generation of which
had not then been demonstrated by the microscope to be governed by the
same laws.

Lamarck has, indeed, attempted to raise an argument in favor of his
system, out of the very confusion which has arisen in the study of some
orders of animals and plants, in consequence of the slight shades of
difference which separate the new species discovered within the last
half century. That the emba