Time and Life | Page 6

vast epochs, sometimes through the whole range of recorded time, with
very little change. By reason of this persistency, the typical form of
such a kind might be called a "persistent type," in contradistinction to
those types which have appeared for but a short time in the course of
the world's history. Examples of these persistent types are abundant
enough in both the vegetable and the animal kingdoms. The oldest
group of plants with which we are well acquainted is that of whose
remains coal is constituted; and as far as they can be identified, the
carboniferous plants are ferns, or club-mosses, or Coniferae, in many
cases generically identical with those now living!
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
'Reptilia'--the class which exhibits the largest proportion of entirely
extinct forms of any one type,--that of the 'Crocodilia', has persisted
from at least the commencement of the Mesozoic epoch up to the
present time with so much constancy, that the amount of change which
it exhibits may fairly, in relation to the time which has elapsed, be
called insignificant. And the imperfect knowledge we have of the
ancient mammalian population of our earth leads to the belief that
certain of its types, such as that of the 'Marsupialia', have persisted with
correspondingly little change through a similar range of time.
Thus it would appear to be demonstrable, that, notwithstanding the
great change which is exhibited by the animal population of the world
as a whole, certain types have persisted comparatively without
alteration, and the question arises, What bearing have such facts as

these on our notions of the history of life through geological time? The
answer to this question would seem to depend on the view we take
respecting the origin of species in general. If we assume that every
species of animal and of plant was formed by a distinct act of creative
power, and if the species which have incessantly succeeded one another
were placed upon the globe by these separate acts, then the existence of
persistent types is simply an unintelligible irregularity. Such
assumption, however, is as unsupported by tradition or by Revelation
as it is opposed by the analogy of the rest of the operations of nature;
and those who imagine that, by adopting any such hypothesis, they are
strengthening the hands of the advocates of the letter of the Mosaic
account, are simply mistaken. If, on the other hand, we adopt that
hypothesis to which alone the study of physiology lends any
support--that hypothesis which, having struggled beyond the reach of
those fatal supporters, the Telliameds and Vestigiarians, who so nearly
caused its suffocation by wind in early infancy, is now winning at least
the provisional assent of all the best thinkers of the day--the hypothesis
that the forms or species of living beings, as we know them, have been
produced by the gradual modification of pre-existing species--then the
existence of persistent types seems to teach us much. Just as a small
portion of a