ndants remained
creeping forms. The vertebrates alone remained swimming, and
probably neither they nor their descendants ever crept until they
emerged on the land, or as amphibia were preparing for land
life. If this be true, it is a fact worthy of our most careful
consideration. The swimming life would appear to be neither as easy
nor as economical as the creeping. It is certainly hard to believe
that food would not have been obtained with less effort and in
greater abundance at the bottom than in the water above. The
swimming life gave rise to higher and stronger forms; but did its
maintenance give immediate advantage in the struggle for existence?
This is an exceedingly interesting and important question, and
demands most careful consideration. But we shall be better prepared
to answer it in a future lecture.

The period of development of mollusks, articulates, and vertebrates,
is really one. They developed to a certain extent contemporaneously.
The development of vertebrates was slow, and they were the last to
appear on the stage of geological history.

You must all have noticed that development, during this period,
takes on a much more hopeful form than during that described in the
last chapter. Then digestion and reproduction were dominant. Now
muscle is of the greatest importance. If this fails of development,
as in mollusks, the group is doomed to degeneration or at best
stagnation. But we have seen the dawn of a still higher function. In
insects and vertebrates the brain is becoming of importance, and
absorbing more and more material. This is the promise of something
vastly higher and better. Better sense-organs are appearing, fitted
to aid in a wider perception of more distant objects. The vertebrate
has discovered the right path; though a long journey still lies
before it. The night is far spent, the day is at hand.

CHAPTER IV

VERTEBRATES: BACKBONE AND BRAIN

In tracing man's ancestry from fish upward we ought properly to
describe three or four fish, an amphibian, a reptile, and then take
up the series of mammalian ancestors. But we have not sufficient
time for so extended a study, and a simpler method may answer our
purpose fairly well. Let us fix our attention on the few organs
which still show the capacity of marked development, and follow each
one of these rapidly in its upward course.

We must remember that there are changes in the vegetative organs.
The digestive and excretory systems