.
THE SEA 'BOTTOM
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59
and changesin temperature are primarily responsible for
'
the great differences in the faunas of tropical,ten‘1perate and
'
polar regions—differences in the "‘ horizontal "’ distribution
of animals.
Temperature and depth are the factors of
greatest importance controlling the “
vertical
”
distribution
of animals from the shore 'into'deep'water. Owing to the
'
decrease in temperature, the'horizontal differences become
less and less as the Water gets deeper, thus we nd similar
animals at great depths in» the polar and equatorial regions
'
because the temperature is the same, While animals found in
'
shallow water in temperate seas, for example, have relatives
living in deeper water with a similar temperature in the
tropics.
'
'
,
The shallow waters of the globe can be —divided into
different regions corresponding to changes in the hori—
zontal distribution of animals, the result, aswe have seen, of
differences in temperature.
These, it must be noted, do not
follow parallels of latitude, but are greatly inuenced by cold
and hot Currents, an example—ofwhich is provided by the
western coasts of Europe ‘bathed bÿ the warm Gulf Stream
and the frozen coasts of Labrador—in similar latitudes—
which_are washed bythe cold Labrador current.
We can
between an Arctic region, including the water
round the North Pole and “ boreal ”
areas along the west
coast of Europe and in_the North Pacic ; an ludo—Pacic
Region including the sho‘res of India, East Africa, China, the
_
East Indie_s and Australia ;- :a West American Region along
the tropical shores of West Amenca'; an East American
'
Region running southward from Newfoundland; a West
African
both the Mediterranean and the
Guinea coast; ‘ and nally an Antarctic’ Region which
includes the southern Coasts of Australia, Africa, and South
America from the Argentine on the east to Ecuador on the
west.
Within any. onearea the members of the marine