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 vertebræ 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 scale. On the contrary, the predaceous cephalopods and the
highly organized crustaceous are among the oldest fossils. Such appears
to be the order of nature as evidenced by facts, and it must be
admitted, however repugnant to preconceived notions or mere mortal
conjectural amendments.

In the third place the evidence seems to preponderate in favour of
_permanency of species_. There can be no doubt that both plants and
animals may, by the influence of breeding, and of external agents
operating upon their constitution, be greatly modified, so as to give
rise to varieties and races different from what before existed. But
there are limits to such modifications, as in the different kind and
breed of dogs; and no organized beings can, by the mere working of