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INTRODUCTION.
sibility, of many other and more perfect structures
having been formed elsewhere at the same early period
of the world's history. The maxim " de non apparen-
-"
tibus et non existentibns eadem est ratio is scarcely
applicable to geological cases of this nature.
The conditions which exist in one part of the sea-bed
are often quite different in another part. The late Professor
Forbes, in his valuable Report to the British
Association in 1843 on the Invertebrata of the iEgean,
stated his belief that the zero of animal life was probably
about 300 fathoms, because his dredgings in that
sea at a depth of 230 fathoms yielded but very few
species. But in other tracts of the ocean living animals
of various kinds have been repeatedly obtained from far
greater depths. Our knowledge of abyssal life is only
checked by the difficulty of such explorations and by
the imperfect nature of our means of discovery.
It is
a high and worthy object of the naturalist's ambition,
and by no means devoid of general interest.
Speculations
ancients. In the f
" There is a magnet-like attraction in
These waters to the imaginative power
That links the viewless with the visible,
And pictures tilings unseen."
of this kind were not unknown to the
Halieutica \ of Oppian, written nearly
seventeen centuries ago, it is stated that no one had
found the bottom of the sea and that the ;
greatest depth
ascertained by man was 300 fathoms, where Amphitrite
had been seen. But this grand discovery does
not seem to have satisfied the poetical philosopher, and
he enters into a long disquisition as to the many other
wonderful things that may be concealed in the recesses
of the boundless ocean—
adding, however,
"
. . i . . oXtyos $e voos fiepoireGOL tcai i. "
okici}.