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1859
1860
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in the Old World can 1861 1866
in the Old World could 1859 1860
can 1869 1872

hotter than any 1859 1860 1861 1866
OMIT 1869 1872

yet 1859 1860 1861 1866
hotter than any in the New World, but 1869
hotter than any in the New World; but 1872

or flora. 1859 1860 1861 1866
different from that of the surrounding districts; for it is very rare to find a group of organisms confined to a small area, having conditions peculiar in only a slight degree. 1869
different from that of the surrounding districts; for it is rare to find a group of organisms confined to a small area, of which the conditions are peculiar in only a slight degree. 1872

inhabit a 1859 1860 1861
are separated by a space of ten degrees of latitude and live under a 1866
are separated by a space of ten degrees of latitude and are exposed to 1869 1872

climate, and they will be found 1859 1860 1861
climate, yet they are 1866
conditions, yet they are 1869
conditions; yet they are 1872

climate. 1860 1861 1866 1869 1872
climate. Analogous facts could be given with respect to the inhabitants of the sea. 1859

small areas in the Old World can be pointed out hotter than any in the
Old
New
World
World,
yet these are not inhabited by a
peculiar
peculiar
fauna or flora. Notwithstanding this
general parallelism
parallelism
in the conditions of the Old and New Worlds, how widely different are their living productions!
In the southern hemisphere, if we compare large tracts of land in Australia, South Africa, and western South America, between latitudes
25°
25°
and
35°,
35°,
we shall find parts extremely similar in all their conditions, yet it would not be possible to point out three faunas and floras more utterly dissimilar.
Or,
Or
again,
again
we may compare the productions of South America south of lat.
35°
35°
with those north of
25°,
25°,
which consequently inhabit a considerably different climate, and they will be found incomparably more closely related to each
other,
other
than they are to the productions of Australia or Africa under nearly the same climate. Analogous facts could be given with respect to the inhabitants of the sea.
A second great fact which strikes us in our general review is, that barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions of various regions. We see this in the great difference
in
of
nearly all the terrestrial productions of the New and Old Worlds, excepting in the northern parts, where the land almost joins, and where, under a slightly different climate, there might have been free migration for the northern temperate forms, as there now is for the strictly arctic productions. We see the same fact in the great difference between the inhabitants of Australia, Africa, and South America under the same
latitude;
latitude:
for these countries are almost as much isolated from each other as is possible. On each continent, also, we see the same fact; for on the opposite sides of