not
surprised to find the coiled type (Goniatites) gain upon and gradually
replace the straight-shelled types (Orthoceratites). The Silurian
ocean swarms with these great shelled Cephalopods, of which the little
Nautilus is now the only survivor.

We will not enlarge on the Sponges and Corals, which are slowly
advancing toward the higher modern types. Two new and very powerful
organisms have appeared, and merit the closest attention. One is the
fish, the remote ancestor of the birds and mammals that will one day
rule the earth. The other may be the ancestor of the fish itself, or it
may be one of the many abortive outcomes and unsuccessful experiments of
the stirring life of the time. And while these new types are themselves
a result of the great and stimulating changes which we have reviewed
and the incessant struggle for food and safety, they in turn enormously
quicken the pace of development. The Dreadnought appears in the
primitive seas; the effect on the fleets of the world of the evolution
of our latest type of battleship gives us a faint idea of the effect, on
all the moving population, of the coming of these monsters of the deep.
The age had not lacked incentives to progress; it now obtains a more
terrible and far-reaching stimulus.

To understand the situation let us see how the battle of land and sea
had proceeded. The Devonian Period had opened with a fresh emergence of
the land, especially in Europe, and great inland seas or lakes were left
in the hollows. The tincture of iron which gives a red colour to our
characteristic Devonian rocks, the Old Red Sandstone, shows us that
the sand was deposited in inland waters. The fish had already been
developed, and the Devonian rocks show it swarming, in great numbers and
variety, in the enclosed seas and round the fringe of the continents.

The first generation was a group of strange creatures, half fish and
half Crustacean, which are known as the Ostracoderms. They had large
armour-plated heads, which recall the Trilobite, and suggest that they
too burrowed in the mud of the sea or (as many think) of the inland
lakes, making havoc among the shell-fish, worms, and small Crustacea.
The hind-part of their bodies was remarkably fish-like in structure. But
they had no backbone--though we cannot say whether they may not have
had a rod of cartilage along the back--and no articulated jaws like the
fish. Some regard them as a connecting link between the Crustacea
and the