re any
vertebrates worthy of the name. If any were present, their skeleton
was purely cartilaginous and not preserved.

I think we may go farther, although in this latter consideration we
may very possibly be mistaken. We have already seen that the
progress made by any animal may be measured more or less accurately
by the length of time during which its ancestors maintained a
swimming life. The ancestors of the coelenterates settled to the
bottom first. Then successively those of flatworms, mollusks,
annelids, and crabs. All this time the ancestors of vertebrates were
swimming in the water above. Food was probably more abundant,
certainly more easily and economically obtained by a creeping life,
on the bottom. But thither the vertebrate could not go. There his
mail-clad competitors were too strong for him. Those which settled
and tried to compete in this sort of life perished. We may have to
except the ascidia, but they paid for their success by the loss of
nearly all their vertebrate characteristics. The future progress of
vertebrates depended upon their continual activity in the swimming
life. And they were forced by their environment to maintain this.
Otherwise they might, probably would, never have attained their
present height of organization. Certainly at this time you would
have found it hard to believe that the victory was to fall to these
weaker and smaller vertebrates.

Let us come down to a later period. Reptiles, mammals, and birds are
struggling for supremacy. Of the power and diversity of form of
these old reptiles we have generally no adequate conception. The
forms now living are but feeble remnants. There were huge
sea-serpents, and forms like our present crocodiles, but far more
powerful. Others apparently resembled in form and habit the
herbivorous and carnivorous mammals of to-day. Others strode or
leaped on two legs. And still others flew like bats or birds. They
were terrible forms, with coats of mail and powerful jaws and teeth.
And they were active and swift. When we look at them we see that the
vertebrate, though slow in gaining the lead, is sure to hold it. The
internal skeleton gave fewer advantages at the start; its greatest
superiority had lain in future possibilities.

But which vertebrate is heir to the future? It would have been a
hard choice between reptile and bird. I feel sure that I, for one,
should not have selected the mammal, a small, feeble being, hiding
in holes and ledges, a