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 suf