O2 ON THE PERSISTENT TYPES OF ANIMAL LIFE 
are wonderfully like the millepores of our own seas, as every one may 
convince himself who compares Heézolites with Helvopora. 
Turning to the J7Zollusca, the genera Crania, Discina, Lingula, 
have persisted from the Silurian epoch to the present day, with so 
little change, that very competent malacologists are sometimes puzzled 
to distinguish the ancient from the modern species. Mautzlz have 
a like range, and the shell of the liassic Lo/zgo is similar to that of the 
“squid” of our own seas. Among the Axnulosa, the carboniferous 
insects are in several cases referable to existing genera, as are the 
Arachnida, the highest group of which, the scorpions, is represented 
in the coal by a genus differing from its living congeners only in the 
disposition of its eyes. 
The vertebrate subkingdom furnishes many examples of the same 
kind. The Ganotdet and Elasmobranchit are known to have persisted 
from at least the middle of the Paleozoic epoch to our own times, 
without exhibiting a greater amount of deviation from the typical 
characters of these orders, than may be found within their limits at 
the present day. 
Among the Repézlza, the highest group, that of the Crocodilia, was 
represented at the beginning of the Mesozoic epoch, if not earlier, 
by species identical in the essential character of their organization 
with those now living, and presenting differences only in such points 
as the form of the articular faces of their vertebra, in the extent 
to which the nasal passages are separated from the mouth by bone, 
and in the proportions of the limbs. Even such imperfect knowledge 
as we possess of the ancient mammalian fauna leads to the belief that 
certain of its types, such as that of the M/arsupialia, have persisted 
with no greater change through as vast a lapse of time. 
It is difficult to comprehend the meaning of such facts as these, 
if we suppose that each species of animal and plant, or each great 
type of organization, was formed and placed upon the surface of 
the globe at long intervals by a distinct act of creative power; and 
it is well to recollect that such an assumption is as unsupported 
by tradition or revelation as it is opposed to the general analogy 
of Nature. 
If, on the other hand, we view “ Persistent Types,” in relation to 
that hypothesis which supposes the species of living beings living at 
any time to be the result of the gradual modification of pre-existing 
species—a hypothesis which, though unproven and sadly damaged by 
some of its supporters, is yet the only one to which physiology lends 
any countenance—their existence would seem to show, that the 
