rmation after the earliest and
simplest fishes, is, considering how little we know of the space of
time represented by a formation, not early: their being later in
any degree is the fact mainly important. The subsequent rise of
new orders of fishes, fully piscine in character, may be explained
by the supposition of their having been developed, as is most
likely, from a different portion of the inferior sub-kingdom. In
short, all the objections which have been made to the great fact of
a general progress of organic development throughout the geological
ages, will be found, on close examination, to refer merely to
doubtful appearances of small moment, which vanish into nothing
when rightly understood."

Upon some of the chief points here involved, it may be remarked that the
most eminent physiologists are not agreed; they are not agreed that
animals can be arranged in a series, passing from lower to higher; nor
that animals of a higher kind in the embryo state pass through the
successive stages of the lower kinds; the character of these stages, in
the asserted doctrine, being taken from the brain and heart, and man
being the highest point of the series. There are physiologists too who
deny that the brain of the human embryo at any period, however early,
resembles the brain of any mollusk or of any articulata. It never, they
assert, passes through a stage comparable or analogous to a permanent
condition of the same organ in any invertebrate animal; and in like
manner the spinal cord in the human vertebrae at no period agrees with
the corresponding part of the lower kind of animals. The moment it
becomes visible in the human embryo, it is entirely dorsal in position;
while in mollusks and articulatas a great part, or nearly the whole, is
ventral. The same is true of the heart, or centre of the vascular
system, which has always a different relative position in the great
nervous centre in the human embryo from what it has in any articulate
animal, and in most mollusks.

A second position in the _Vestiges_ appears not to have been
established--namely, as to the uniform geological arrangement of
different organic structures. It is not true that _only_ the lowest
forms of animal life are found in the lowest fossiliferous rocks, and
that the more complicated structures are gradually and exclusively
developed among the higher bands in what might be called a natural
ascending