in the Amphibian. The
body is raised up higher from the ground, on firmer limbs; the ribs and
the shoulder and pelvic bones--the saddles by which the weight of the
body is adjusted between the limbs and the backbone--are strengthened
and improved. Finally, two important organs for the protection and
nurture of the embryo (the amnion and the allantois) make their
appearance for the first time in the reptile. In grade of organisation
the reptile is really nearer to the bird than it is to the salamander.

Yet these Permian reptiles are so generalised in character and so
primitive in structure that they point back unmistakably to an Amphibian
ancestry. The actual line of descent is obscure. When the reptiles first
appear in the rocks, they are already divided into widely different
groups, and must have been evolved some time before. Probably they
started from some group or groups of the Amphibia in the later
Carboniferous, when, as we saw, the land began to rise considerably.
We have not yet recovered, and may never recover, the region where the
early forms lived, and therefore cannot trace the development in detail.
The fossil archives, we cannot repeat too often, are not a continuous,
but a fragmentary, record of the story of life. The task of the
evolutionist may be compared to the work of tracing the footsteps of a
straying animal across the country. Here and there its traces will be
amply registered on patches of softer ground, but for the most part they
will be entirely lost on the firmer ground. So it is with the fossil
record of life. Only in certain special conditions are the passing forms
buried and preserved. In this case we can say only that the Permian
reptiles fall into two great groups, and that one of these shows
affinities to the small salamander-like Amphibia of the Coal-forest (the
Microsaurs), while the other has affinities to the Labyrinthodonts.

A closer examination of these early reptiles may be postponed until we
come to speak of the "age of reptiles." We shall see that it is probable
that an even higher type of animal, the mammal, was born in the throes
of the Permian revolution. But enough has been said in vindication of
the phrase which stands at the head of this chapter; and to show how
the great Primary age of terrestrial life came to a close. With its new
inhabitants the earth enters upon a fresh phase, and thousands of its
earlier animals and plants are sealed in their primordial tombs, to
a