er, rounded, and simply lobed. If
some feet from the same plant the roots succeed in pushing into a
soil only damp, without being submerged, their stalks then are
short, none of their leaves are divided into capillary divisions,
which gives rise to _Ranunculus hederaceus_, which the botanists
regard as a species whenever they meet with it.

"There is no doubt that as regards animals important changes in the
circumstances under which they are accustomed to live do not produce
alteration in their organs; for here the changes are much slower in
operating than in plants, and, consequently, are to us less marked,
and their cause less recognizable.

"As to the circumstances which have so much power in modifying the
organs of living beings, the most influential are, doubtless, the
diversity of the surroundings in which they live; but besides this
there are many others which, in addition, have a considerable
influence in the production of the effects in question.

"It is known that different localities change in nature and quality
owing to their position, their nature, and their climate, as is
easily seen in passing over different places distinguished by
special features; hence we see a cause of variation for the animals
and plants which live in these different places. But what we do not
sufficiently know, and even what we generally refuse to believe, is
that each place itself changes with time in exposure, in climate, in
nature, and quality, although with a slowness so great in relation
to our own continuance that we attribute to it a perfect stability.

"Now, in either case, these changed localities proportionally change
the circumstances relative to the organisms which inhabit them, and
the latter then give rise to other influences bearing on these same
beings.

"We perceive from this that, if there are extremes in these changes,
there are also gradations--namely, degrees which are intermediate
and which fill the interval. Consequently there are also gradations
in the differences which distinguish what we call _species_.

"It is then evident that the whole surface of the earth offers, in
the nature and situation of the matters which occupy its different
points, a diversity of circumstances which is throughout in relation
with that of the forms and parts of animals, independent of the
special diversity which necessarily results from the progress o