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this we find has been the case; 1859 1860 1861 1866 1869
they have been modified; 1872

though very 1859 1860 1861
one with another, though 1866 1869 1872

and some few are 1859 1860
and many are 1861
or sub-species, and some as certainly 1866 1869
or sub-species, and some as 1872

species. 1859 1860 1861
each other on the several ranges. 1866 1869 1872

illustrating what, as I believe, actually took place during the Glacial period, I 1859 1860 1861 1866
the foregoing illustration I have 1869 1872

the 1859 1860 1861 1866
of our imaginary Glacial period, the 1869 1872

the foregoing remarks on distribution apply not only to strictly arctic forms, but also to 1859 1860 1861 1866
it is necessary also to 1869
it is also necessary to assume that 1872

for some of these are 1859 1860 1861 1866 1869
were 1872

lower mountains and 1859 1860 1861
lower mountain-slopes and 1866 1869
world, for some of the species which now exist 1872

plains 1859 1860 1861 1866 1869
lower mountain-slopes and on the plains 1872

and 1859 1860 1861 1866 1869
are the same; and 1872

different;
ferent;
for it is not likely that all the same arctic species will have been left on
mountain-ranges
mountain ranges
far distant
distant
from each other, and have survived there ever since; they
will
will,
also
also,
in all
probability,
probability
have become mingled with ancient Alpine species, which must have existed on the mountains before the commencement of the Glacial epoch, and which during
the
its
coldest period will have been temporarily driven down to the plains; they will, also, have been
subsequently exposed
exposed
to somewhat different climatal influences. Their mutual relations will thus have been in some degree disturbed; consequently they will have been liable to modification; and this we find has been the case; for if we compare the present Alpine plants and animals of the several great European
mountain-ranges
mountain-ranges,
though very many of the species
still remain
remain
are
identically the same, some
exist as
present
varieties, some
are ranked
are ranked
as doubtful
forms
forms,
and some few are distinct yet closely allied
species
or
representing
representative
species.
In illustrating what, as I believe, actually took place during the Glacial period, I
have assumed
assumed
that at
the
its
commencement the arctic productions were as uniform round the polar regions as they are at the present day. But the foregoing remarks on distribution apply not only to strictly arctic forms, but also to
include many
many
sub-arctic and
to
to
some few
northern
northern
temperate
forms
forms,
for some of these are the same
round
on
the lower mountains and on the plains of North America and
Europe
Europe;
and it may be
reasonably
reasonably
asked how I account for
this
the necessary
degree of uniformity
in
of
the sub-arctic and
northern
northern
temperate forms round the world, at the commencement of the
real Glacial
Glacial
period. At the present day, the sub-arctic and northern temperate productions of the Old and New Worlds are separated from each other by the
whole Atlantic
Atlantic
Ocean and by the
extreme
extreme
northern part of the Pacific. During the Glacial period, when the
in-
in-