1434 
THE VOYAGE OF H.M.S. CHALLENGEE. 
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forming on the summit, and the mud-line is met with on either side of this ridge at 
about 300 fathoms. In basin-like depressions within the 100-fathom line — like the 
Silver Pits of the North Sea — mud is formed, while it cannot rest on the rims of these 
basins. All the minute organie particles washed down from the land, carried away from 
the shallow waters by currents, or derived from the decay and death of pelagic organisms, 
ultimately find a resting place on the bottom in deep water, principally just about and 
beyond the mud-line. Here is situated the great feeding ground in the ocean. When 
tow-nets are dragged a foot or two immediately over this mud deposit myriads of young 
and adult Crustaceans are captured, nearly all of the red or brown colour characteristic 
of deep water, such as species of Calanus, Euchaeta, Pasiphaea, Crangon, Calocaris, 
Pamlahis, Ilippohjte, many Amphipods, Isopods, and immense numbers of Schizopods. 
Fishes and Cephalopods are likewise abundant and are captured along with the 
Crustaceans when the trawl can be dragged near, but without touching, the bottom. 
The Crustaceans, many of them furnished with phosphorescent organs, are scavengers, 
and feed upon the organic particles that fall from the surface or are washed from 
.shallower waters seawards and finally settle on the bottom in the quiet deep waters about 
and beyond the mud-line. In their turn these Crustaceans, and the other organisms 
about the mud-line furnish most abundant food for many migratory species, such as 
the herring and the salmon. The stomachs of whales and narwhals are likewise fre- 
(juently crammed with Cephalopods, Schizopods, Pasiphseas, and Calanids of a deep-red 
colour, evidently devoured in depths of several hundred fathoms. It has been observed 
that ascending bodies of water, produced by tidal curre'nts or by strong winds, frequently 
bring great numbers of the young and immature individuals of these mud-line animals 
into the surface and sub-surface waters near land masses. The majority of the animals 
living about and beyond the oceanic mud-line appear to have a direct development or 
have no free-swimming larval stage, and the same is the case with deep-sea and 
shallow- water polar animals. From these and other considerations it seems legitimate 
to suggest that these marine faunas are genetically connected with, and were originally 
derived from, the mud-line fauna of the present period and of the not very remote 
geological past. On the other hand, the great majority of the animals attached to or 
living on the hard bottom in shallow water above and within the mud-line in sub-tropical 
and e.specially in tropical and coral-reef regions, have pelagic larvae, and were probably 
for the most jiart derived from the Mud-line fauna at a much more ancient date. 
The difficulties connected with trawling and dredging in deep water are no doubt 
mu< h greater than in shallow depths, and on the whole the explorations in very deep 
water have been rather limited ; but taking all this, as well as the number of the 
( 'hallenger’s trawlings and dredgings in each zone of depth into consideration, it may be 
regarded as a well-established fact that the aggregate number of species and individuals is 
