eedingly promising
path, but it led to the bottom of a cliff, not to the summit.

The mollusks, clams, and snails took an easier, down-hill road. They
formed a shell, and it developed large enough to cover them. It
hampered and almost destroyed locomotion and reduced nerve to a
minimum. But nerves are nothing but a nuisance anyhow. And why
should they move? Food was plenty down in the mud, and if danger
threatened, they withdrew into the shell. They stayed down in the
mud and let the world go its way. If grievously afflicted by a
parasite they produced a pearl--to save themselves from further
discomfort. They developed just enough muscle and nervous system to
close the shell or drag it a little way; that was all. Digestion and
reproduction retained the supremacy. They were fruitful and
multiplied, and produced hosts of other clams and snails. The
present was enough for them and they had that.

For if the winner in the struggle for existence is the one who gains
the most food, the most entire protection against discomfort, danger
from enemies or unfavorable surroundings, and the most fruitful and
rapid reproduction--and these are all good--then the clam is the
highest product of evolution. It never has been surpassed--I venture
to say it never can be--except possibly by the tape-worms. I can
never help thinking with what contempt these primitive oysters, if
they had had brains enough, would have looked down upon the toiling,
struggling, discontented, fighting, aspiring primitive vertebrates.
How they would have wondered why God allowed such disagreeable,
disturbing, unconventional creatures to exist, and thanked him that
he had made the world for them, and heaven too, if there be such a
place for mollusks. Their road led to the Slough of Contentment.

But even in molluscan history there was a tragic chapter. The squids
and cuttle-fishes regained the swimming life, and in their latest
forms gave up the protective shell. But its former presence had so
modified their structure that any great advance was impossible. It
was too late. The sins of the fathers were visited upon the children
in the thousandth generation.

The vertebrate developed an internal skeleton. This was necessarily
a slow growth, and the type came late to supremacy. The longitudinal
muscles are arranged in heavy bands on each side of the back, and
the animal swims rapidly. The sense-organs are keen. The brain
contains the ganglia of several or many se