stand much sifting, seeing that the Macrurous Podophthalmia depart as
far in one direction from the common type of Podophthalmia, or from any
embryonic condition of the Brachyura, as the Brachyura do in the other;
and that the middle terms between Macrura and Brachyura--the
Anomura--are little better represented in the older Mesozoic rocks than
the Brachyura are.

None of the cases of progressive modification which are cited from among
the Invertebrata appear to me to have a foundation less open to
criticism than these; and if this be so, no careful reasoner would, I
think, be inclined to lay very great stress upon them. Among the
Vertebrata, however, there are a few examples which appear to be far
less open to objection.

It is, in fact, true of several groups of Vertebrata which have lived
through a considerable range of time, that the endoskeleton (more
particularly the spinal column) of the older genera presents a less
ossified, and, so far, less differentiated, condition than that of the
younger genera. Thus the Devonian Ganoids, though almost all members
of the same sub-order as 'Polypterus', and presenting numerous
important resemblances to the existing genus, which possesses biconcave
vertebrae, are, for the most part, wholly devoid of ossified vertebral
centra. The Mesozoic Lepidosteidae, again, have, at most, biconcave
vertebrae, while the existing 'Lepidosteus' has Salamandroid,
opisthocoelous, vertebrae. So, none of the Paleozoic Sharks have shown
themselves to be possessed of ossified vertebrae, while the majority of
modern Sharks possess such vertebrae. Again, the more ancient
Crocodilia and Lacertilia have vertebrae with the articular facets of
their centra flattened or biconcave, while the modern members of the
same group have them procoelous. But the most remarkable examples of