from
the egg to its adult size. Such facts should make those who rest
their fanciful theories of the origin and development of life on the
imperfection of the geological record, filling up the supposed lapses to
suit themselves, more cautious as to their results.

We have found, then, Radiates, Mollusks, and Articulates in plenty;
and now what is to be said of Vertebrates in these old times,--of the
highest and most important division of the Animal Kingdom, that to which
we ourselves belong? They were represented by Fishes alone; and the Fish
chapter in the history of the early organic world is a curious, and,
as it seems to me, a very significant one. We shall find no perfect
specimens; and he would be a daring, not to say a presumptuous thinker,
who would venture to reconstruct a fish of the Silurian age from any
remains that are left to us. But still we find enough to indicate
clearly the style of those old fishes, and to show, by comparison with
the living types, to what group of modern times they belong. We should
naturally expect to find the Vertebrates introduced in their simplest
form; but this is by no means the case: the common fishes, as Cod,
Herring, Mackerel, and the like, were unknown in those days.

But there are two groups of so-called fishes, differing from these by
some marked features, among which we may find the modern representatives
of these earliest Vertebrates. Of these two groups one consists chiefly
now of the Gar-Pikes of our Western waters, though the Sturgeons share
also in some of their features. In these fishes there is a singular
union of reptilian with fish-like characters. The systems of circulation
and of respiration in them are more complicated than in the common
fishes; the structure of the skull resembles that of the skull in
reptiles, and they have other reptilian characters, such as their
ability to move the head upon the neck independently of the body, and
the connection of the vertebrae by ball-and-socket joint, instead of
by inverted cones, as in the ordinary fishes. Their scales are also
peculiar, being covered by enamel so hard, that, if struck with steel,
they will emit sparks like flint. It is on account of this peculiarity
that the whole group has been called Ganoid. Now, though we have
not found as yet any complete specimens of Silurian fishes, their
disconnected remains are scattered profusely in the early deposits. The
scales, parts of the backbone, parts of the skull,