with many of the other authorities whose opinions have been cited, completely
ignored the researches of Sir John Eoss, pubhshed more than twenty years
previously (it being distinctly stated in Professor Ehrenberg’s communication
to the ‘Annals and Magazine of Natural History,’ from which the last extracts
have been made, that 190 and 270 fathoms were “ the greatest depths that had ”
previously to 1844 “ been sounded ”), not one of those writers has, up to the
present hour, recognized the validity of Professor Ehrenberg’s reasoning with
reference to the vitality of creatui*es belonging to the very lowest type, and
therefore much less likely to be affected by conditions which they contend
would prove fatal to creatures of a higher order.
Having thus placed before the reader the grounds on which naturalists have
heretofore regarded the deeper abysses of the ocean as unfitted for the support
of animal life, and having endeavoured to state fairly the value of the evidence
adduced hy the only two observers whose researches have been directed towards
the establishment of an opposite view, I have now to draw attention to the
physical conditions by which the geographical distribution and the duration on the
earth of marine creatures are determined, and to the various influences which, in
conformity with the most recent discoveries, appear to regulate their bathymetrical
range.
I t would be foreign to the purpose of the present inquiry to state the various
arguments by which the theory of transmutability of species and the doctrine of
specific centres of creation have been maintained by their respective supporters.
I t is sufficient to know that, commencing from an assumed period in the earth’s
history, no matter how remote from “ the beginning,” certain forms were
grouped together within fixed geographical areas, each of which was already
distinguished by typical characters. Were it possible to define this period, or to
adopt a cotemporaneous starting-point for every group of animate forms on the
surface of the globe, whence to calculate the amount of divergence or specific
differentiation its several species had undergone, the task of determining which
hypothesis is true and which false would be comparatively easy. But, in the
absence of such a fixed point, it only remains for us to draw our inferences from
well-marked modifications in the characters of well-known species, and endeavour
to reconcile these modifications with such altered conditions of the earth’s crust
as we can prove to have accompanied them.
When we consider the changes which are continuously and yet almost imperceptibly
going on in the distribution of land and sea, and bear in mind that,
although the periods occupied in the completion of these are inconceivably
vast, they are insignificant in comparison with epochs in the world’s history
anteriorly elapsed, we shall understand how gradual must be the operation of
causes by which the characters of species are modified and their disappearance
from the earth eventually brought about. Were it otherwise, all the individuals
belonging to a species in any given zoological province would leave their remains
within the narrow stratum of deposit on which they had lived. But this
happens only in exceptional cases ; and hence we meet with fossil remains of
species extending frequently through strata of such immense thickness as to
prove, in conjunction with what is known of the rate at which those strata are
formed, that vast changes in the relative distribution of sea and land must have
occurred before they became extinct.
Bearing this fact in mind, it is necessary to avoid the very common error of
taking for granted that the ancestors of animals living at the present time under
a set of recognized conditions must have lived under similar conditions since the
period at which they first appeared on the eai'th. The fossil remains of the
older extinct forms, both of animals and plants, clearly show how different must
have been the condition of the earth’s surface when they peopled it. But we
have only to look at the changes observable duiing much more recent periods,
in order to be satisfied that species still in existence must have passed through
repeated and critical alterations in the conditions by which they were surrounded;
and in such cases we might naturally expect to find structural
modifications to have taken place in a greater or less degree. A time will in all
probability arrive when, by a further series of changes, these existing forms will
in turn become scarcer and scarcer, and then finally disappear from the earth.
The extinction of certain Struthious birds is well known to have been completed
within a very recent period ; and although in some examples human agency has
been instrumental in producing this result, there is no reason to believe that in
the case of the gigantic Struthious forms of New Zealand, or in that of the
Great Awk of the Arctic regions, extinction has not been consequent on natural
causes. But, supposing changes on the earth’s surface and climates to have been
moderate in extent and duration, it is evident that creatures may have survived