Among animals, instances of the same kind may be found in every
sub-kingdom. The 'Globigerina' of the Atlantic soundings is identical
with that which occurs in the chalk; and the casts of lower silurian
'Foraminifera', which Ehrenberg has recently described, seem to
indicate the existence at that remote period of forms singularly like
those which now exist. Among the corals, the palaeozoic 'Tabulata' are
constructed on precisely the same type as the modern millepores; and if
we turn to molluscs, the most competent malacologists fail to discover
any generic distinction between the 'Craniae', 'Lingulae' and
'Discinae' of the silurian rocks and those which now live. Our
existing 'Nautilus' has its representative species in every great
formation, from the oldest to the newest; and 'Loligo', the squid of
modern seas, appears in the lias, or at the bottom of the mesozoic
series, in a form, at most, specifically different from its living
congeners. In the great assemblage of annulose animals, the two highest
classes, the insects and spider tribe, exhibit a wonderful persistency
of type. The cockroaches of the carboniferous epoch are exceedingly
similar to those which now run about our coal-cellars; and its locusts,
termites and dragon-flies are closely allied to the members of the same
groups which now chirrup about our fields, undermine our houses, or
sail with swift grace about the banks of our sedgy pools. And, in like
manner, the palaeozoic scorpions can only be distinguished by the eye
of a naturalist from the modern ones.

Finally, with respect to the 'Vertebrata', the same law holds good:
certain types, such as those of the ganoid and placoid fishes, having
persisted from the palaeozoic epoch to the present time without a
greater amount of deviation from the normal standard than that which is
seen within the limits of the group as it now exists. Even among the