ggle 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 (Na