ud.
"Requiescat in pace."

But zooelogy has its tragedies as well as human history. Let us turn
to the development of a third molluscan line terminating in the
cuttle-fishes. The ancestors of these cephalopods, although still
possessed of a shell and a high visceral hump, regained the swimming
life. First, apparently, by means of fins, and then by a simple but
very effective use of a current of water, they acquired an often
rapid locomotion. The highest forms gave up the purely defensive
campaign, developed a powerful beak, led a life like that of the old
Norse pirates, and were for a time the rulers and terrors of the
sea. With their more rapid locomotion the supra-oesophageal
ganglion reached a higher degree of development, and it was served
by sense-organs of great efficiency. They reduced the external
shell, and succeeded, in the highest forms, of almost ridding
themselves of this burden and encumbrance. Traces of it remain in
the squids, but transformed into an internal quill-like, supporting,
not defensive, skeleton. They have retraced the downward steps of
their ancestors as far as they could. And the high development of
their supra-oesophageal ganglion and sense-organs, and their
powerful jaws and arms, or tentacles, show to what good purpose they
have struggled. But the struggle was in vain, as far as the
supremacy of the animal kingdom was concerned. Their ancestors had
taken a course which rendered it impossible for their descendants to
reach the goal. Their progress became ever slower. They were
entirely and hopelessly beaten by the vertebrates. They struggled
hard, but too late.

The history of mollusks is full of interest. They show clearly how
intimately nervous development is connected with the use of the
locomotive organs. The snail crept, and slightly increased its
nervous system and sense-organs. The clam almost lost them in
connection with its stationary life. The cephalopods were
exceedingly active, developed, therefore, keen sense-organs and a
very large and complicated supra-oesophagal ganglion, which we
might almost call a brain.

The articulate series consists of two groups of animals. The higher
group includes the crabs, spiders, thousand-legs, and finally the
insects, and forms the kingdom of arthropoda. The lower members are
still usually reckoned as worms, and are included under the
annelids. Of these our common earthworm is a good example, and near
them belong the leeches. But the mar