For there is great diversity in this
respect, most of the Mediterranean, for instance, having a scanty
Plankton as compared with the North Sea. In the South Pacific, west of
Patagonia, there is said to be an immense "sea desert" where there is
little Plankton, and therefore little in the way of fishes. The success
of fisheries in the North, e.g. on the Atlantic cod-banks, is due to the
richness of the floating sea-meadows and the abundance of the smaller
constituents of the animal Plankton.

Hunger is plain enough when the Baleen Whale rushes through the water
with open jaws, engulfing in the huge cavern of its mouth, where the
pendent whalebone plates form a huge sieve, incalculable millions of
small fry.

But there is love as well as hunger in the open sea. The maternal care
exhibited by the whale reaches a very high level, and the delicate shell
of the female Paper Nautilus or Argonaut, in which the eggs and the
young ones are sheltered, may well be described as "the most beautiful
cradle in the world."

Besides the permanent inhabitants of the open sea, there are the larval
stages of many shore-animals which are there only for a short time. For
there is an interesting give and take between the shore-haunt and the
open sea. From the shore come nutritive contributions and minute
organisms which multiply quickly in the open waters. But not less
important is the fact that the open waters afford a safe cradle or
nursery for many a delicate larva, e.g. of crab and starfish,
acorn-shell and sea-urchin, which could not survive for a day in the
rough-and-tumble conditions of the shore and the shallow water. After
undergoing radical changes and gaining strength, the young creatures
return to the shore in various ways.

III. THE DEEP SEA

Very different from all the other haunts are the depths of the sea,
including the floor of the abysses and the zones of water near the
bottom. This haunt, forever unseen, occupies more than a third of the
earth's surface, and it is thickly peopled. It came into emphatic notice
in connection with the mending of telegraph cables, but the results of
the _Challenger_ expedition (1873-6) gave the first impressive picture
of what was practically a new world.

Physical Conditions

The average depth of the ocean is about two and a half miles; therefore,
since many parts are relatively shallow, there must be enormous depths.
A few of these, technically called "deeps," are about six miles