iantly at the height of from four to five thousand feet
on the lower slopes of the Himalaya, but with perhaps a still greater
preponderance of temperate forms. So again in the mountainous island of
Fernando Po, in the Gulf of Guinea, Mr. Mann found temperate European
forms beginning to appear at the height of about five thousand feet. On
the mountains of Panama, at the height of only two thousand feet, Dr.
Seemann found the vegetation like that of Mexico, "with forms of the
torrid zone harmoniously blended with those of the temperate."

Now let us see whether Mr. Croll's conclusion that when the northern
hemisphere suffered from the extreme cold of the great Glacial period,
the southern hemisphere was actually warmer, throws any clear light on
the present apparently inexplicable distribution of various organisms
in the temperate parts of both hemispheres, and on the mountains of the
tropics. The Glacial period, as measured by years, must have been very
long; and when we remember over what vast spaces some naturalised plants
and animals have spread within a few centuries, this period will have
been ample for any amount of migration. As the cold became more and more
intense, we know that Arctic forms invaded the temperate regions; and
from the facts just given, there can hardly be a doubt that some of the
more vigorous, dominant and widest-spreading temperate forms invaded the
equatorial lowlands. The inhabitants of these hot lowlands would at the
same time have migrated to the tropical and subtropical regions of the
south, for the southern hemisphere was at this period warmer. On the
decline of the Glacial period, as both hemispheres gradually recovered
their former temperature, the northern temperate forms living on the
lowlands under the equator, would have been driven to their former homes
or have been destroyed, being replaced by the equatorial forms returning
from the south. Some, however, of the northern temperate forms would
almost certainly have ascended any adjoining high land, where, if
sufficiently lofty, they would have long survived like the Arctic
forms on the mountains of Europe. They might have survived, even if the
climate was not perfectly fitted for them, for the change of temperature
must have been very slow, and plants undoubtedly possess a certain
capacity for acclimatisation, as shown by their transmitting to their
offspring different constitutional powers of resisting heat and cold.

In the regula