612 
NATURE 
[ Oct. 22, 1885 
shallower water. These numbers are not final, but the propor- 
tions are not likely to be greatly altered when the whole of the 
Challenger Reports are completed. These facts may be in part 
explained by the greater abundance of food present in the con- 
tinental aris which forms the chief constituent of the terrigenous 
deposits ; but it is probably more closely connected with the 
greater distance of the seaward stations from the original place of 
migration. We must suppose that all deep-sea animals have 
been derived originally from shallow water; those which de- 
scended first into deeper water have, generally speaking, been 
able to migrate to a greater distance seawards than those which 
set out later, and being derived from older stocks they have 
retained in the great deeps some of the characters which are 
now regarded as archaic and embryonic. 
Although no new types of structure have been discovered in 
organisms from the deep sea, the peculiar modifications which 
animals have undergone to accommodate themselves to abysmal 
conditions are sufficiently interesting and remarkable ; the eyes 
of some fish and crustaceans have become atrophied or have 
disappeared altogether, while in others they have become of 
exceedingly large size or have been so modified as to be scarcely 
recognisable as eyes : for instance, in the case of the scopelid fish 
/pnops ; fins and antenne have become extraordinarily elongated 
and at times‘appear to simulate the alcyonarians of the deep sea. 
The higher crustacea and some families of fish have very few 
and very large eggs in the deep-sea species, while their shallow- 
water representatives have a very large number of very small eggs, 
showing apparently that the deep-sea species have relatively 
few enemies. While some groups, for instance the Pycno- 
gonids, Tubularians, and Nudibranchs, have much more 
gigantic representatives in the deep sea than in shallow water, 
the representatives of the majority of groups, and especially the 
Gasteropods and Lamellibranchs, are much smaller, and gener- 
ally speaking have a dwarfed and delicate appearance, the shells 
being poorly supplied with carbonate of lime. Indeed the solid 
tissues of most deep-sea animals are but feebly developed when 
compared with shallow-water forms. The experienced dredger 
has, asa rule, little difficulty in recognising a deep-sea species in 
a dredging from its:general appearance. Many deep-sea animals 
emit, and some have special organs for the emission of, phos- 
phorescent light, which appears to play a large 7é/e in the 
economy of deep-sea life. 
One of the most striking facts with respect to deep-sea 
animals is their very wide distribution—the same species being 
found in all the great ocean basins. At the depth of half a mile 
identical species are dredged off the coast of Scotland and off 
the coast of Australia at the Antipodes ; the nearly uniform con- 
ditions, existing everywhere at depths greater than half a mile, 
facilitates the wide distribution of species which have once 
accommodated themselves to a life at that depth. The same 
consideration probably explains the occurrence of some identical 
and nearly identical species in the shallow waters of the temperate 
and polar regions of both hemispheres. 
Among the higher crustacea the Brachyurans, which are 
regarded as a modern group, are found in great numbers in 
shallow waters, but have very few representatives in deep 
waters, and appear to be quite absent from the abysmal regions. 
On the other hand, the representatives of the Schizopoda, 
Anomoura, and Macrura, which are regarded as older groups, 
are widely distributed in the deep sea; many similar instances 
of this kind could be given. The stalked Crinoids, the Elpididee 
among the Holothurians, the Pourtalesiz and Phormosomas 
among the Echinids, and other groups, have now no repre- 
sentatives in depths less than 100 fathoms, but are widely dis- 
tributed in all greater depths ; while many genera are confined 
to the abysmal regions. We are not as yet, however, in a 
position to fully discuss many curious points in distribution, even 
did time permit. 
It may be urged that after all the few hundred scrapings of 
our small trawls and dredges can give but a very inadequate idea 
of the condition of things over the millions of square miles 
covered by the ocean, but against this it may be argued with 
great force that as the same animals and deposits occurred again 
and again with little variation, we doubtless have even now a 
tolerably complete knowledge of deep-sea life. 
When we turn to the surface waters, one may exclaim: it is a 
dull and stupid soul that would not rejoice at the first acquaint- 
ance with the teeming pelagic life of the ocean, rich in bizarre 
forms and varied colours, or that would not be struck with 
wonder at the magnificent displays of phosphorescent light sent 
forth on a dark night from the surface of an equatorial ocean, 
like flashes of “‘ spirits from the vasty deep.” 
“p, 
3eyond the shadow of the ship 
1 watched the water snakes ; 
They moved in tracks of shining white, 
And when they reared the elfish light 
Fell off in hoary flakes. 
““ Within the shadow of the ship 
I watched their rich attire ; 
Blue, glossy green, and velvet black, 
They coiled and swam, and every track 
Was a flash of golden fire. 
““Oh, happy living things! No tongue 
Their beauty might declare. 
A spring of love gushed from my heart, 
And I blessed them unaware.” 
Experiments with tow-nets have shown that life exists in all 
the intermediate waters of the ocean, between the surface and 
the bottom, yet sparingly tlere when compared with what occurs 
just above the bottom, or more markedly when compared with 
the abundant and luxurious development of life in the surface 
and sub-surface waters. 
In mid-ocean the majority of the organisms are quite distinct 
from those usually found along the coasts in bays and estuaries, 
though, like the deep-sea animals, they were, in all probability, 
originally derived from the shallow waters around the continents. 
There are species of diatoms, calcareous and other alge, many 
foraminifera, siphonophora, a few annelids, many crustaceans, 
numerous pteropods, heteropods, and other molluscs, the pelagic 
tunicates, and many fishes whose home is in the great systems of 
oceanic currents. It is only occasionally, or in special localities, 
that some of the species are borne to continental shores, for the 
members of this oceanic pelagic fauna and flora appear to be killed 
off where the ocean is affected by the fresh waters from the land. 
In the equatorial regions the species and individuals are most 
abundant, and they vary with temperature, latitude, and the 
salinity of the water. 
In the Antarctic or Southern Ocean diatoms abound at the 
surface, and in the same region the sea-floor is covered with 
their dead siliceous frustules, which form a diatom ooze. In the 
middle and western Pacific, where the surface water is less salt 
than in the Atlantic, the radiolarians, which likewise secrete silica 
from sea water, occur in vast numbers at the surface and in 
intermediate waters, and in these regions their dead shells 
and skeletons make up the chief part of the deep-sea deposits, 
known as radtolarian ooze. 
But it is those species belonging to the varied pelagic oceanic 
organisms which secrete lime for their shells and skeletons that 
are principally forced on our attention, both from their pro- 
digious numbers and the pact played by their remains in the 
formation of deposits. These species flourish especially in the 
warmest and saltest waters. In a square mile of equatorial 
water 600 feet deep it is estimated that there are over 16 tons of 
carbonate of lime in the form of shells, which belong to about 
30 species of calcareous Algze, Foraminifera, Pteropods, and 
Heteropods. When these surface organisms die and fall to the 
bottom they form the deposits known as fferopod and globi- 
gerina oozes. In descending they, as well as other surface 
organisms, carry down with them some of the organic matter of 
their tissues, which, not decomposing rapidly in the cold deep 
water, forms the chief source of nourishment for deep-sea 
animals, and the chlorophyll which Prof. Hartley has discovered 
in some deep-sea deposits is probably derived from diatoms 
which have fallen to the bottom in this way. 
It is, however, a very remarkable fact that the dead shells of 
these Foraminifera and Pteropods are not found on the bottom 
of the sea beneath all the regions where they flourish abundantly 
at the surface. They are found at greater depths beneath warm 
equatorial waters than elsewhere, but there is barely a trace of 
them in all the greatest depths, although in an adjacent area, where 
the surface and intermediate conditions are the same, but where 
the depth is less than three miles, they may make up 75 or even 
go per cent. of the deposit. It has been abundantly proved that 
when sea water, and especially sea water containing absorbed 
carbonic acid, passes over a dead shell or coral, the lime is 
gradually removed, being carried away by the water as bicarbonate 
in solution ; and the shell or coral is removed more rapidly the 
more surface it presents to the water in proportion to the 
amount of carbonate of lime present in the shell. This is what 
| happens to pelagic shells as they fall through the water to the 
