3. A third haunt of life is the floor of the Deep Sea, the abyssal area,
which occupies more than a half of the surface of the globe. It is a
region of extreme cold--an eternal winter; of utter darkness--an eternal
night--relieved only by the fitful gleams of "phosphorescent" animals;
of enormous pressure--2-1/2 tons on the square inch at a depth of 2,500
fathoms; of profound calm, unbroken silence, immense monotony. And as
there are no plants in the great abysses, the animals must live on one
another, and, in the long run, on the rain of moribund animalcules which
sink from the surface through the miles of water. It seems a very
unpromising haunt of life, but it is abundantly tenanted, and it gives
us a glimpse of the insurgent nature of the living creature that the
difficulties of the Deep Sea should have been so effectively conquered.
It is probable that the colonising of the great abysses took place in
relatively recent times, for the fauna does not include many very
antique types. It is practically certain that the colonisation was due
to littoral animals which followed the food-débris, millennium after
millennium, further and further down the long slope from the shore.