egalichthys of the Coal
Measures, with its various carboniferous congeners, with the genera
Diplopterus, Dipterus, and Osteolepis of the Old Red Sandstone,--all
brilliantly enamelled fish,--are thickly pore-covered. But whatever
purpose these pores may have served, it seems in the Secondary period to
have been otherwise accomplished, if, indeed, it continued to exist. It
is a curious circumstance, that in no case do the pores seem to pass
_through_ the scale. Whatever their use, they existed merely as
communications between the cells of the middle cancellated layer and the
surface. In a fish of the Chalk,--_Macropoma Mantelli_,--the exposed
fields of the scales are covered over with apparently hollow, elongated
cylinders, as the little tubes in a shower-bath cover their round field
of tin, save that they lie in a greatly flatter angle than the tubes;
but I know not that, like the pores of the Dipterians and the
Megalichthys, they communicated between the interior of the scale and
its external surface. Their structure is at any rate palpably different,
and they bear no such resemblance to the pores of the human skin as that
which the Palaeozoic pores present.

The amount of design exhibited in the scales of some of the more ancient
ganoids,--design obvious enough to be clearly read,--is very
extraordinary. A single scale of _Holoptychius Nobilissimus_,--fast
locked up in its red sandstone rock,--laid by, as it were, for
ever,--will be seen, if we but set ourselves to unravel its texture, to
form such an instance of nice adaptation of means to an end as might of
itself be sufficient to confound the atheist. Let me attempt placing one
of these scales before the reader, in its character as a flat counter of
bone, of a nearly circular form, an inch and a half in diameter, and an
eighth-part of an inch in thickness; and then ask him to bethink
himself of the various means by which he would impart to it the greatest
possible degree of strength. The human skull consists of two tables of
solid bone, an inner and an outer, with a spongy cellular substance
interposed between them, termed the _diploe_; and such is the effect of
this arrangement, that the blow which would fracture a continuous wall
of bone has its force broken by the spongy intermediate layer, and
merely injures the outer table, leaving not unfrequently the inner one,
which more especially protects the brain, wholly unharmed. Now, such
also was the arrangement in th