arch introduced in almost every possible form and
modification, and the utmost flexibility secured to their stony arms by
the amazing number of the pieces of which they were composed, and the
nice disposition of the joints. In the Pentacrinites of the Secondary
period (see Fig. 97) an immense spread of arms, about a thousand in
number, and composed of about a hundred thousand separate pieces, had
all the flexibility, though formed of solid lime, of a _drift_ of nets,
and yet were so nicely jointed, tooth fitting into tooth in all their
numerous parts, and the whole so bound together by ligament, that, with
all the flexibility, they had also all the toughness and tenacity, of
pieces of thread network. Human ingenuity, with the same purposes to
effect, that is, the sweeping of shoals of swimming animals into a
central receptacle, would probably construct a somewhat similar machine;
but it would take half a lifetime to execute one equally elaborate.

[Illustration: Fig. 94.

AMMONITES HUMPHRIESIANUS.

(_Oolite._)]

[Illustration: Fig. 95.

ENCRINITES MONILIFORMIS.

(_Trias._)]

[Illustration: Fig. 96.

CUPRESSOCRINUS CRASSUS.

(_Old Red Sandstone._)]

[Illustration: Fig. 97.[21]

PENTACRINUS FASCICULOSUS.

(_Lias._)]

[Illustration: Fig. 98.

_a_, CHAMFERED SCALES. (_Osteolepis._)

_b_, IMBRICATED SCALES. (_Glyptolepis._)

(_Old Red Sandstone._)]

In carefully examining, for purposes of restoration, some of the
earliest ganoidal fishes, I was not a little impressed by the peculiar
mechanical contrivances exhibited in their largely developed dermal
skeletons. In some cases these contrivances were sufficiently simple,
resembling those which we find exemplified in the humbler trades,
originated in comparatively unenlightened ages; and yet their simplicity
had but the effect of rendering the peculiarly _human_ cast of the mind
exhibited in their production all the more obvious. The bony scales
which covered fishes such as the Osteolepis and Diplopterus of the Old
Red Sandstone, or the Megalichthys of the Coal Measures, were of
considerable mass and thickness. They could not, compatibly with much
nicety of finish, be laid over each other, like the thin horny scales of
the salmon or herring; and so we find them curiously fitted together,
not like slates on a modern roof, but like hewn stones on an ancient
one. There ran on the upper surface of each, along the anterior side and
higher end, a groove of a d