of the sea has been finally settled and for all depths, for
there is no reason to suppose that the depth anywhere exceeds between
three and four thousand fathoms; and if there be nothing in the
conditions of a depth of 2,500 fathoms to prevent the full development of
a varied Fauna, it is impossible to suppose that even an additional
thousand fathoms would make any great difference."[5]

[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind,
obtained by previous observers, are stated at length in the sixth
chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under
the authority of Professor Peirce, the Superintendent of the United
States Coast Survey, in the years 1867, 1868, and 1869, are particularly
noteworthy, and it is probably not too much to say, in the words of
Professor Agassiz, "that we owe to the coast survey the first broad and
comprehensive basis for an exploration of the sea bottom on a large
scale, opening a new era in zoological and geological research."]

As Dr. Wyville Thomson's recent letter, cited above, shows, the use of
the trawl, at great depths, has brought to light a still greater
diversity of life. Fishes came up from a depth of 600 to more than 1,000
fathoms, all in a peculiar condition from the expansion of the air
contained in their bodies. On their relief from the extreme pressure,
their eyes, especially, had a singular appearance, protruding like great
globes from their heads. Bivalve and univalve mollusca seem to be rare at
the greatest depths; but starfishes, sea urchins and other echinoderms,
zoophytes, sponges, and protozoa abound.

It is obvious that the _Challenger_ has the privilege of opening a new
chapter in the history of the living world. She cannot send down her
dredges and her trawls into these virgin depths of the great ocean
without bringing up a discovery. Even though the thing itself may be
neither "rich nor rare," the fact that it came from that depth, in that
particular latitude and longitude, will be a new fact in distribution,
and, as such, have a certain importance.

But it may be confidently assumed that the things brought up will very
frequently be zoological novelties; or, better still, zoological
antiquities, which, in the tranquil and little-changed depths of the
ocean, have escaped the causes of destruction at work in the shallows,
and represent the predominant population of a past age.

It has been seen that Audouin and Milne