and Macrura; while several of the Brachyura, which
appear in the Chalk, belong to existing genera; and none exhibit either
an intermediate, or an embryonic, character.

The VERTEBRARA.--Among fishes I have referred to the Coelacanthini
(comprising the genera 'Coelacanthus', 'Holophagus', 'Undina', and
'Macropoma') as affording an example of a persistent type; and it is
most remarkable to note the smallness of the differences between any of
these fishes (affecting at most the proportions of the body and fins,
and the character and sculpture of the scales), notwithstanding their
enormous range in time. In all the essentials of its very peculiar
structure, the 'Macropoma' of the Chalk is identical with the
'Coelacanthus' of the Coal. Look at the genus 'Lepidotus', again,
persisting without a modification of importance from the Liassic to the
Eocene formations inclusive.

Or among the Teleostei--in what respect is the 'Beryx' of the Chalk
more embryonic, or less differentiated, than 'Beryx lineatus' of King
George's Sound?

Or to turn to the higher Vertebrata--in what sense are the Liassic
Chelonia inferior to those which now exist? How are the Cretaceous
Ichthyosauria, Plesiosauria, or Pterosauria less embryonic, or more
differentiated, species than those of the Lias?

Or lastly, in what circumstance is the 'Phascolotherium' more
embryonic, or of a more generalized type, than the modern Opossum; or a
'Lophiodon', or a 'Paleotherium', than a modern 'Tapirus' or 'Hyrax'?

These examples might be almost indefinitely multiplied, but surely they
are sufficient to prove that the only safe and unquestionable testimony
we can procure--positive evidence--fails to demonstrate any sort of
progressive modification towards a less embryonic, or less generalised,
type in a great many groups of animals of long-continued geological
existence. In these groups there is abundant evidence of variation--none
of what is ordinarily understood as progression; and, if the known
geological record is to be regarded as even any considerable fragment
of the whole, it is inconceivable that any theory of a necessarily
progressive development can stand, for the numerous orders and families
cited afford no trace of such a process.

But it is a most remarkable fact, that, while the groups which have
been mentioned, and many besides, exhibit no sign of progressive
modification, there are others, co-existing with them, under the same
conditions, in whi