individual specimens are absolutely alike, or differ so little that the
differences can hardly be perceived, they must be classed as of the same
species; if the differences begin to be perceptible, but if at the same
time there is more resemblance than difference, the individuals
presenting these features should be classed as of a different species,
but as of the same genus; if the differences are still more marked, but
nevertheless do not exceed the resemblances, then they must be taken as
not only specific but generic, though as not sufficient to warrant
the individuals in which they appear, being placed in different
classes. If they are still greater, then the individuals are not even
of the same class; but it should be always understood that the
resemblances and differences are to be considered in reference to the
entirety of the plant or animal, and not in reference to any particular
part only.[68] The two rocks which are equally to be avoided are, on
the one hand, absence of method, and, on the other, a tendency to
over-systematize.[69]

Like Dr. Erasmus Darwin, and more recently Mr. Francis Darwin, Buffon is
more struck with the resemblances than with the differences between
animals and plants, but he supposes the vegetable kingdom to be a
continuation of the animal, extending lower down the scale, instead of
holding as Dr. Darwin did, that animals and vegetables have been
contemporaneous in their degeneration from a common stock.

"We see," he writes, "that there is no absolute and essential difference
between animals and vegetables, but that Nature descends by subtle
gradations from what we deem the most perfect animal to one which is
less so, and again from this to the vegetable. The fresh-water polypus
may perhaps be considered as the lowest animal, and as at the same time
the highest plant."[70]

Looking to the resemblances between animals and plants, he declares that
their modes of reproduction and growth involve such close analogy that
no difference of an essential nature can be admitted between them.[71]

On the other hand, Buffon appears, at first sight, to be more struck
with the points of difference between the mental powers of the lower
animals and man than with those which they present in common. It is
impossible, however, to accept this as Buffon's real opinion, on the
strength of isolated passages, and in face of a large number of others
which point stealthily but irresistibly to an exactly oppo