Very different from all the other haunts are the depths of the sea,
including the floor of the abysses and the zones of water near the
bottom. This haunt, forever unseen, occupies more than a third of the
earth's surface, and it is thickly peopled. It came into emphatic notice
in connection with the mending of telegraph cables, but the results of
the _Challenger_ expedition (1873-6) gave the first impressive picture
of what was practically a new world.