According to Darwin, the struggle for existence, as a big fact in the
economy of Animate Nature, includes not only competition but all the
endeavours which secure the welfare of the offspring, and give them a
good send-off in life. So it is without a jolt that we pass from
struggle for food and foothold to parental care. The marine leech called
Pontobdella, an interesting greenish warty creature fond of fixing
itself to skate, places its egg-cocoons in the empty shell of a bivalve
mollusc, and guards them for weeks, removing any mud that might injure
their development. We have seen a British starfish with its fully-formed
young ones creeping about on its body, though the usual mode of
development for shore starfishes is that the young ones pass through a
free-swimming larval period in the open water. The father sea-spider
carries about the eggs attached to two of his limbs; the father
sea-horse puts his mate's eggs into his breast pocket and carries them
there in safety until they are hatched; the father stickleback of the
shore-pools makes a seaweed nest and guards the eggs which his wives are
induced to lay there; the father lumpsucker mounts guard over the bunch
of pinkish eggs which his mate has laid in a nook of a rocky shore-pool,
and drives off intruders with zest. He also aerates the developing eggs
by frequent paddling with his pectoral fins and tail, as the Scots name
Cock-paidle probably suggests. It is interesting that the salient
examples of parental care in the shore-haunt are mostly on the male
parent's side. But there is maternal virtue as well.
[Illustration: TEN-ARMED CUTTLEFISH OR SQUID IN THE ACT OF CAPTURING A
FISH
The arms bear numerous prehensile suckers, which grip the prey. In the
mouth there are strong jaws shaped like a parrot's beak. The
cuttlefishes are molluscs and may be regarded as the highest of the
backboneless or Invertebrate animals. Many occur near shore, others in
the open sea, and others in the great depths.]
[Illustration: GREENLAND WHALE
Showing the double blowhole or nostrils on the top of the head and the
whalebone plates hanging down from the roof of the mouth.]
[Illustration: MINUTE TRANSPARENT EARLY STAGE OF A SEA-CUCUMBER
It swims in the open sea by means of girdles of microscopic cilia shown
in the figure. After a period of free swimming and a remarkable
metamorphosis, the animal settles down on the floor of the sea in
relatively shallow water.]
[Illustration: _Photo: British Museum (Natural History)_
AN INTRICATE COLONY OF OPEN-SEA ANIMALS (_Physophora Hydrostatica_)
RELATED TO THE PORTUGUESE MAN-OF-WAR
There is great division of labor in the colony. At the top are floating
and swimming "persons"; the long ones below are offensive "persons"
bearing batteries of stinging cells; in the middle zone there are
nutritive, reproductive, and other "persons." The color of the colony is
a fine translucent blue. Swimmers and bathers are often badly stung by
this strange animal and its relatives.]
[Illustration: A SCENE IN THE GREAT DEPTHS
Showing a deep-sea fish of large gape, two feather-stars on the end of
long stalks, a "sea-spider" (or Pycnogon) walking on lanky legs on the
treacherous ooze, likewise a brittle-star, and some deep-sea corals.]
The fauna of the shore is remarkably _representative_--from unicellular
Protozoa to birds like the oyster-catcher and mammals like the seals.
Almost all the great groups of animals have apparently served an
apprenticeship in the shore-haunt, and since lessons learned for
millions of years sink in and become organically enregistered, it is
justifiable to look to the shore as a great school in which were gained
racial qualities of endurance, patience, and alertness.