ations of
individuals of the same race should have been kept in captivity for
a considerable time, there is no doubt but that even the form of the
parts of these individuals would gradually undergo notable changes.
For a much stronger reason, if, instead of a simple captivity
constantly maintained over them, this circumstance had been at the
same time accompanied by a change to a very different climate, and
if these individuals by degrees had been habituated to other kinds
of food, and to other kinds of movements to obtain it; certainly
these circumstances, united and becoming constant, would insensibly
form a new and special race.

"Where do we find, in nature, this multitude of races of _dogs_,
which, as the result of domesticity to which we have reduced these
animals, have been brought into their present condition? Where do we
find these bull-dogs, greyhounds, water spaniels, spaniels,
pug-dogs, etc., etc., races which present among themselves much
greater differences than those which we admit to be specific in wild
animals of the same genus?

"Without doubt, a primitive single race, very near the wolf, if it
is not itself the true type, has been submitted by man, at some
period, to the process of domestication. This race, which then
offered no difference between its individuals, has been gradually
dispersed by man into different countries, with different climates;
and after a time these same individuals, having undergone the
influences of their habitats, and of the different habits they were
obliged to contract in each country, have undergone remarkable
changes, and have formed different special races. Now, the man who,
for commercial reasons or from interests of any other kind, travels
a very great distance, having carried into a densely populated
place, as for example a great capital, different races of dogs
originated in some very distant country, then the increase of these
races by heredity (_generation_) has given rise successively to all
those we now know.

"The following fact proves, as regards plants, how a change in any
important circumstance leads to a change in the parts of their
organisms.

"So long as _Ranunculus aquatilis_ is submerged in the water, its
leaves are all finely incised and the divisions hair-like; but when
the stalks of this plant reach the surface of the water, the leaves
which grow out in the air are wid