ia we have the
Oriental region very fairly defined; so that the relation of the
geographical with the zoological primary divisions of the earth is
sufficiently clear. In order to make these relations visible to the eye and
more easily remembered, we will put them into a tabular form:

Regions. Geographical Equivalent.
Palaearctic EUROPE, with north temperate Africa and Asia.
Ethiopian AFRICA (south of the Sahara) with Madagascar.
Oriental TROPICAL ASIA, to Philippines and Java.
Australian AUSTRALIA, with Pacific Islands, Moluccas, &c.
Nearctic NORTH AMERICA, to North Mexico.
Neotropical SOUTH AMERICA, with tropical N. America and W. Indies.

The following arrangement of the regions will indicate their geographical
position, and to a considerable extent their relation to each other.

N E A R C T I C--P A L A E A R C T I C
| | |
| | ORIENTAL
| ETHIOPIAN |
NEO- |
TROPICAL AUSTRALIAN

May 4th. Diameter of spot 31deg 24'
June 4th. ,, ,, 28deg 0'
,, 17th. ,, ,, 22deg 54'
July 4th. ,, ,, 18deg 24'
,, 12th. ,, ,, 15deg 20'
,, 20th. ,, ,, 18deg 0'

We thus see that Mars has two permanent snow-caps, of nearly equal size in
winter but diminishing very unequally {55} in summer, when the southern cap
is reduced to nearly one third the size of the northern; and this fact is
held by Mr. Carpenter, as it was by the late Mr. Belt, to be opposed to the
view of the hemisphere which has winter in _aphelion_ (as the southern now
has both in the Earth and Mars), having been alone glaciated during periods
of high excentricity.[9]

Before, however, we can draw any conclusion from the case of Mars, we must
carefully scrutinise the facts, and the conditions they imply. In the first
place, there is evidently this radical difference between the state of Mars
now and of the Earth during a glacial period--that Mars has no great
ice-sheets spreading over its temperate zone, as the Earth undoubtedly had.
This we know from the fact of the _rapid_ disappearance of the white
patches over a belt three degrees wide in a fortnight (equal to a width of
about 100 miles of our measure), and in the northern hemisphere of eight
degrees wide