late Corals have existed from the
Silurian epoch to the present day, but I am not aware that the ancient
_Heliolites_ possesses a single mark of a more embryonic or less
differentiated character, or less high organization, than the existing
_Heliopora_. As for the Aporose Corals, in what respect is the Silurian
_Paloeocydus_ less highly organized or more embryonic than the modern
_Fungia_, or the Liassic Aporosa than the existing members of the same
families?

The _Mollusca_.--In what sense is the living _Waldheimia_ less
embryonic, or more specialized, than the palaeozoic _Spirifer_; or the
existing _Rhynchonellae_, _Craniae_, _Discinae_, _Lingulae_, than the
Silurian species of the same genera? In what sense can _Loligo_ or
_Spirula_ be said to be more specialized, or less embryonic, than
_Belemnites_; or the modern species of Lamellibranch and Gasteropod
genera, than the Silurian species of the same genera?

The ANNULOSA.--The Carboniferous Insecta and Arachnida are
neither less specialized, nor more embryonic, than those that now live,
nor are the Liassic Cirripedia 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 VERTEBRATA.--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