nimals and plants exhibit traces of
a parallel advance of the physical conditions and the organic structure.
The general principle, he inculcates, is, that each animal of a higher
kind, in the progress of its embryo state, passes through states which
are the final condition of the lower kind; that the higher kinds of
animals came later, and were developed from the lower kinds, which came
earlier in the series of rock formations, by new peculiar conditions
operating upon the embryo, and carrying it to a higher stage. These
conclusions the author maintains geology has established, and of the
results thence derived he gives the subjoined recapitulation:--

"In pursuing the progress of the development of both plants and
animals upon the globe, we have seen an advance in both cases, from
simple to higher forms of organization. In the botanical department
we have first sea, afterwards land plants; and amongst these the
simpler (cellular and cryptogamic) before the more complex. In the
department of zoology, we see, first, traces all but certain of
infusoria [shelled animalculae]; then polypiaria, crinoidea, and
some humble forms of the articulata and mollusca; afterwards higher
forms of the mollusca; and it appears that these existed for ages
before there were any higher types of being. The first step forward
gives fishes, the humblest class of the vertebrata; and, moreover,
the earliest fishes partake of the character of the lower
sub-kingdom, the articulata. Afterwards come land animals, of which
the first are reptiles, universally allowed to be the type next in
advance from fishes, and to be connected with these by the links of
an insensible gradation. From reptiles we advance to birds, and
thence to mammalia, which are commenced by marsupialia,
acknowledgedly low forms in their class. That there is thus a
progress of some kind, the most superficial glance at the
geological history is sufficient to convince us."

Now this appears plausible and conclusive, but the correctness of the
recapitulation here made, and its conformity to actual nature, have been
sharply disputed. It may be true that sea plants came first, but of this
there is no proof; and of land plants there is not a shadow of evidence
that the simpler forms came into being before the more complex: the
simple and complex forms are found together in the more ancient