throw a long line for a Halibut, while with a common fishing-rod he will
catch plenty of Perch from the rocks near the shore; and the differently
colored bands of sea-weed revealed by low tide, from the green line of
the Ulvas through the brown zone of the common Fucas to the rosy and
purple hued sea-weeds of the deeper water show that the florae as well
as the faunae of the ocean have their precise boundaries. This wider
or narrower range of marine animals is in direct relation to their
structure, which enables them to bear a greater or less pressure of
water. All fishes, and, indeed, all animals having a wide range of
distribution in ocean-depths, have a special apparatus of water-pores,
so that the surrounding element penetrates their structure, thus
equalizing the pressure of the weight, which is diminished from without
in proportion to the quantity of water they can admit into their bodies.
Marine animals differ in their ability to sustain this pressure, just
as land animals differ in their power of enduring great variations of
climate and of atmospheric pressure.

Of all air-breathing animals, none exhibits a more surprising power of
adapting itself to great and rapid changes of external influences than
the Condor. It may be seen feeding on the sea-shore under a burning
tropical sun, and then, rising from its repast, it floats up among the
highest summits of the Andes and is lost to sight beyond them, miles
above the line of perpetual snow, where the temperature must be lower
than that of the Arctics. But even the Condor, sweeping at one flight
from tropic heat to arctic cold, although it passes through greater
changes of temperature, does not undergo such changes of pressure as a
fish that rises from a depth of sixty-four feet to the surface of the
sea; for the former remains within the air that surrounds our globe,
and therefore the increase or diminution of pressure to which it is
subjected must be confined within the limits of one atmosphere, while