were favourable to life would be vastly increased; that is to say, they would
have two or more directions to select from, and accordingly the risk of extinction
from inorganic causes would be materially lessened; the extension of the
geographical range of a species, under these circumstances, being at the same
time facilitated and expedited.
In the case of marine creatures, the necessity for migration from place to
place in consequence of changes which render residence in particular localities
unsupportable must, for these reasons, occur much less frequently. I t is also
reasonable to suppose that the tendency to extinction of marine as compared with
terrestrial animals, from purely “ inorganic causes,” must be proportionately small,
inasmuch as, the ratio of land and water on the globe being as 3 to 10, terrestrial
animals must be more frequently checked in migrations which might save them
from extinction, by the intervention of an element they are unfitted to encounter.
Again, human agency must operate to a much smaller extent in effecting the
extermination of the smaller and lower forms of the animal kingdom in the
ocean than it is known to have done in the case of creatures inhabiting circumscribed
areas on land, since access to their haunts is, for the most part,
impossible. And further, as there is good ground for believing that, although
the deepest abysses of the ocean have their living occupants, the number of
individuals is in aU probability very large whilst the number of tribes is proportionally
small, the tendency to extinction of certain tribes by furnishing
sustenance to others becomes materially reduced.
Having thus cursorily and, I fear, very imperfectly detailed the chief causes
which are concerned in determining the distribution and duration of marine
species, I have yet to show how they bear on the question of life in the deeper
abysses of the ocean. Before proceeding with this portion of my subject, however,
it is necessary that I should describe, for the information of those who will,
I trust, constitute a large proportion of my readers (namely, students of marine
natui'al history and others who may have opportunities of taking soundings),
the bathymetrical distribution of both the animal and vegetable creation, down
to those depths which it has heretofore been customary to regard as azoic.
The late Professor Edward Forbes was the first to point out that the various
species of marine animals and plants inhabit distinct successive zones or belts,
commencing with high-water mark and extending downwards, as he himself
I defines them, “ to the deepest abysses from which living beings have been
extracted.” There are four of these zones in the European seas, each of which
is marked and may at once be recognized by typical organisms or groups of
organisms peculiar to it and to it only. Some organisms, however, are common
to all the zones, whilst others are only common to two or three.
The first or littoral zone is that which extends between tide-marks, whether
the rise and fall be one foot or fifty.
The second or Laminarían zone extends from low tide-mark to a depth of
about 15 fathoms, and forms the great centre of sea-weeds, “ fishes, mollusks,
Crustaceans, and Invertebrata of all classes, remarkable for the brightness and the
variegation of the patterns of their colouring.”
The third or Coralline zone reaches down to a depth of about 30 fathoms
below the limit of the Laminarían zone. Here both vertebrate and invertebrate
animals are abundant, but plants become scarce.
The fourth or deepest, namely, the deep-coral zone, extends towards that abyss
where, to repeat Professor Forbes’s words, “ life is either extinguished or exhibits
but a few sparks to mark its lingering presence.” I t may be said to reach down
to a depth of from 300 to 550 fathoms in different latitudes, although, according
to Forbes’s observations, its limit falls short of either of these estimates*.
I t will be observed that the vertical limits of each of these zones increases
with the depth; so that whilst the upper has a depth of only a few feet, the
lowest ranges from 100 to 300. “ Specific animal forms,” writes Mr. Austen,
“ decrease rapidly; and just as the sub-aerial zones of vegetation present
us at last, as we ascend, with only such forms as lichens, so at depths of from
70 to 100 fathoms we have the obscure Nullipores as the extreme forms of
marine vegetation ”f .
I shall hereafter show that, at depths vastly exceeding those above alluded to,
animal life is abundantly represented; and, as aheady stated, although the
crowning evidence still remains to be elicited in the case of the Foraminifera and
Polycystina (namely, vital movements after being brought up from the sea-bed),
such evidence has already been elicited in the instance of creatures of a far
higher order, namely, radiate animals—facts being forthcoming to prove that
• Seo ‘ The Natural History of the European Seas,’ by tho late Professor Edward Forbes, p. 24
r< seq. t Ibid. p. 189.
n 2