SUMMARY OF RESULTS. 
1439 
bottom. Indeed, those species which are captured in the trawl when it has been dragged 
near, but has not touched, the bottom, or are captured in traps like those the Prince of 
Monaco has used in deep water, have a much wider distribution than those species which 
live in or fixed to the muds, clays, and oozes. It will thus be seen that in the 
Stations close to each other the number of species common to two Stations is greater than 
when the Stations are further removed from each other, but the larger percentage of 
species common to the Stations in the high northern and high southern latitudes, than 
between either of these and the equatorial Stations, is noteworthy, and seems to indicate 
that a resemblance can be traced in deep water between the organisms of Arctic and 
Antarctic regions. It must be admitted from these considerations that with reference 
to species there is here no striking evidence of a universal deep-sea fauna spread 
all over the floor of the ocean. The same groups of organisms recur, but this is also 
true of animals living not deeper than the mud-line. 
Many of the deep-sea animals, especially those found in very deep water far from 
land, present archaic characters. Discina and other Brachiopods undoubtedly represent 
a very ancient group. The irregular Sea-urchins and siliceous Sponges recall the fossils 
of the chalk. Still it must be admitted that those who expected to find in the deep sea 
remnants of faunas which flourished in very remote geological periods have been much 
disappointed.^ Heliopora, the King-crabs, Lingulas, Trigonias, Amphioxus, Sturgeons, Antiquity of the 
Port Jackson sharks, Ceratodus, Lejndosiren, Protopterus, and other shore and fresh- 
water forms, probably represent older faunas than anything to be found at present in that of Shore 
the deep sea. Sir Wyville Thomson was of opinion that, from the Silurian period to the Faunas. 
present day, there had been, as now, a continuous deep ocean with a bottom tempera- 
ture oscillating about the freezing-point, and that there had always been an abyssal 
fauna." I am rather inclined to think that in Palaeozoic times the ocean basins were 
not so deep as at the present time, that the ocean then had throughout a nearly 
uniform high temperature, and that life was then either absent or represented only by 
bacteria and other low forms in great depths, as ajipears to be the case at present in 
the Black Sea. As in the Black Sea now, so also was there in all likelihood in 
Palaeozoic times insufficient oxygen in deep water to support a deep-sea fauna. From 
many considerations, one is led to suggest that cooling at the poles commenced in early 
Mesozoic times, that cold water, descending then in polar areas, slowly filled the 
greater depths, and by carrying down a more abundant supply of oxygen, life in water 
deeper than the mud-line became possible ; subsequently migrations gradually took place 
from the mud-line into deep regions of the ocean basins. 
The first trawlings and dredgings conducted by the Challenger in comparatively 
^ See ante, p. 103. 
- Zool. Chall. Exp., vol. i. Introd. p. 47. 
