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1860
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plants and allied forms have apparently 1859 1860 1861
plants and allied forms have 1866
or now slightly modified species have 1869
or slightly modified species have 1872

north to 1859 1860 1861
the north to the 1866 1869 1872

became commingled 1859 1860 1861 1866
two sets be- came commingled in the equatorial regions, 1869
two sets became commingled in the equatorial regions, 1872

Glacial 1859 1860 1861 1866
alternations of the Glacial 1869 1872

were 1859 1860 1861 1869 1872
will have been 1866

enabled to beat the less powerful 1859 1860 1861 1866
the more powerful and were able to hold their places on the mountains, and afterwards to migrate southward with the 1869 1872

forms. 1859 1860 1861 1866
forms; but not so the southern in regard to the northern forms. 1869 1872

as we see 1859 1860 1861 1866
we see 1869
OMIT 1872

homes; but the forms, chiefly northern, which had crossed the equator, would travel still
farther
further
from their homes into the more temperate latitudes of the opposite hemisphere. Although we have reason to believe from geological evidence that the whole body of arctic shells underwent scarcely any modification during their long southern migration and re-migration northward, the case may have been wholly different with those intruding forms which settled themselves on the intertropical mountains, and in the southern hemisphere. These being surrounded by strangers will have had to compete with many new forms of life; and it is probable that selected modifications in their structure, habits, and constitutions will have profited them. Thus many of these wanderers, though still plainly related by inheritance to their brethren of the northern or southern hemispheres, now exist in their new homes as well-marked varieties or as distinct species.
It is a remarkable
fact
fact,
strongly insisted on by Hooker in regard to America, and by Alph. de Candolle in regard to Australia, that many more identical plants and allied forms have apparently migrated from the north to the south, than in a reversed direction. We see, however, a few southern
vegetable
vegetable
forms on the mountains of Borneo and Abyssinia. I suspect that this preponderant migration from north to south is due to the greater extent of land in the north, and to the northern forms having existed in their own homes in greater numbers, and having consequently been advanced through natural selection and competition to a higher stage of
perfection,
perfection
or dominating power, than the southern forms. And thus, when
the
they
became commingled during the Glacial
periods,
period,
the northern forms were enabled to beat the less powerful southern forms.
In
Just in
the same manner as we see at the present day,