sort of false vertebra. Hermann
von Meyer, again, to whose luminous researches we are indebted for our
present large knowledge of the organisation of the older Labyrinthodonts,
has proved that the Carboniferous _Archegosaurus_ had very imperfectly
developed vertebral centra, while the Triassic _Mastodonsaurus_ had the
same parts completely ossified.[6]

[Footnote 6: As this Address is passing through the press (March 7,
1862), evidence lies before me of the existence of a new Labyrinthodont
(_Pholidogaster_), from the Edinburgh coal-field with well-ossified
vertebral centra.]

The regularity and evenness of the dentition of the _Anoplotherium_, as
contrasted with that of existing Artiodactyles, and the assumed nearer
approach of the dentition of certain ancient Carnivores to the typical
arrangement, have also been cited as exemplifications of a law of
progressive development, but I know of no other cases based on positive
evidence which are worthy of particular notice.

What then does an impartial survey of the positively ascertained truths
of palaeontology testify in relation to the common doctrines of
progressive modification, which suppose that modification to have taken
place by a necessary progress from more to less embryonic forms, or from
more to less generalised types, within the limits of the period
represented by the fossiliferous rocks?

It negatives those doctrines; for it either shows us no evidence of any
such modification, or demonstrates it to have been very slight; and as to
the nature of that modification, it yields no evidence whatsoever that
the earlier members of any long-continued group were more generalised in
structure than the later ones. To a certain extent, indeed, it may be
said that imperfect ossification of the vertebral column is an embryonic
character; but, on the other hand, it would be extremely incorrect to
suppose that the vertebral columns of the older Vertebrata are in any
sense embryonic in their whole structure.

Obviously, if the earliest fossiliferous rocks now known are coeval with
the commencement of life, and if their contents give us any just
conception of the nature and the extent of the earliest fauna and flora,
the insignificant amount of modification which can be demonstrated to
have taken place in any one group of animals, or plants, is quite
incompatible with the hypothesis that all living forms are the results of
a necessary process of progressive development, e